diff --git a/checker/src/main/java/org/checkerframework/checker/signature/SignatureAnnotatedTypeFactory.java b/checker/src/main/java/org/checkerframework/checker/signature/SignatureAnnotatedTypeFactory.java
index c608b0d2a53..0d0dd126e2a 100644
--- a/checker/src/main/java/org/checkerframework/checker/signature/SignatureAnnotatedTypeFactory.java
+++ b/checker/src/main/java/org/checkerframework/checker/signature/SignatureAnnotatedTypeFactory.java
@@ -84,6 +84,10 @@ public class SignatureAnnotatedTypeFactory extends BaseAnnotatedTypeFactory {
   protected final AnnotationMirror PRIMITIVE_TYPE =
       AnnotationBuilder.fromClass(elements, PrimitiveType.class);
 
+  /** The {@literal @}{@link Identifier} annotation. */
+  protected final AnnotationMirror IDENTIFIER =
+      AnnotationBuilder.fromClass(elements, Identifier.class);
+
   /** The {@link String#replace(char, char)} method. */
   private final ExecutableElement replaceCharChar =
       TreeUtils.getMethod("java.lang.String", "replace", processingEnv, "char", "char");
@@ -209,9 +213,20 @@ public SignatureTreeAnnotator(AnnotatedTypeFactory atypeFactory) {
 
     @Override
     public Void visitBinary(BinaryTree tree, AnnotatedTypeMirror type) {
+
       if (TreeUtils.isStringConcatenation(tree)) {
-        // This could be made more precise.
-        type.replaceAnnotation(SIGNATURE_UNKNOWN);
+        AnnotatedTypeMirror lType = getAnnotatedType(tree.getLeftOperand());
+        AnnotatedTypeMirror rType = getAnnotatedType(tree.getRightOperand());
+
+        // An identifier can end, but not start, with digits
+        if (lType.getPrimaryAnnotation(Identifier.class) != null
+            && (rType.getPrimaryAnnotation(Identifier.class) != null
+                || TypesUtils.isIntegralNumericOrBoxed(rType.getUnderlyingType()))) {
+          type.replaceAnnotation(IDENTIFIER);
+        } else {
+          // This could be made more precise.
+          type.replaceAnnotation(SIGNATURE_UNKNOWN);
+        }
       }
       return null; // super.visitBinary(tree, type);
     }
@@ -231,10 +246,10 @@ public Void visitCompoundAssignment(CompoundAssignmentTree tree, AnnotatedTypeMi
      *
      * <pre><code>
      * {@literal @}InternalForm String internalForm = binaryName.replace('.', '/');
-     * {@literal @}BinaryName String binaryName = internalForm.replace('/', '.');
+     * {@literal @}DotSeparatedIdentifiers String dsi = internalForm.replace('/', '.');
      * </code></pre>
      *
-     * Class.getName and Class.getCanonicalName(): Cwhen called on a primitive type ,the return a
+     * Class.getName and Class.getCanonicalName(): when called on a primitive type, they return a
      * {@link PrimitiveType}. When called on a non-array, non-nested, non-primitive type, they
      * return a {@link BinaryName}:
      *
@@ -276,7 +291,7 @@ public Void visitMethodInvocation(MethodInvocationTree tree, AnnotatedTypeMirror
           type.replaceAnnotation(INTERNAL_FORM);
         } else if ((oldChar == '/' && newChar == '.')
             && receiverType.getPrimaryAnnotation(InternalForm.class) != null) {
-          type.replaceAnnotation(BINARY_NAME);
+          type.replaceAnnotation(DOT_SEPARATED_IDENTIFIERS);
         }
       } else {
         boolean isClassGetName = TreeUtils.isMethodInvocation(tree, classGetName, processingEnv);
diff --git a/checker/tests/signature/Concatenation.java b/checker/tests/signature/Concatenation.java
new file mode 100644
index 00000000000..a8e673b1a6e
--- /dev/null
+++ b/checker/tests/signature/Concatenation.java
@@ -0,0 +1,8 @@
+import org.checkerframework.checker.signature.qual.*;
+
+public class Concatenation {
+
+  @Identifier String m(@Identifier String s, int i) {
+    return s + i;
+  }
+}
diff --git a/framework/src/main/java/org/checkerframework/common/value/ValueAnnotatedTypeFactory.java b/framework/src/main/java/org/checkerframework/common/value/ValueAnnotatedTypeFactory.java
index 4a3a4af2cf1..094ded83315 100644
--- a/framework/src/main/java/org/checkerframework/common/value/ValueAnnotatedTypeFactory.java
+++ b/framework/src/main/java/org/checkerframework/common/value/ValueAnnotatedTypeFactory.java
@@ -641,7 +641,7 @@ public Void visitNewArray(NewArrayTree tree, AnnotatedTypeMirror mirror) {
   /*package-private*/ AnnotationMirror convertSpecialIntRangeToStandardIntRange(
       AnnotationMirror anm, TypeKind primitiveKind) {
     long max = Long.MAX_VALUE;
-    if (TypesUtils.isIntegralPrimitive(primitiveKind)) {
+    if (TypeKindUtils.isIntegral(primitiveKind)) {
       Range maxRange = Range.create(primitiveKind);
       max = maxRange.to;
     }
diff --git a/javacutil/src/main/java/org/checkerframework/javacutil/TypeKindUtils.java b/javacutil/src/main/java/org/checkerframework/javacutil/TypeKindUtils.java
index 12d70478844..c53b6d44d98 100644
--- a/javacutil/src/main/java/org/checkerframework/javacutil/TypeKindUtils.java
+++ b/javacutil/src/main/java/org/checkerframework/javacutil/TypeKindUtils.java
@@ -32,6 +32,25 @@ public static boolean isIntegral(TypeKind typeKind) {
     }
   }
 
+  /**
+   * Return true if the argument is one of INT, SHORT, BYTE, LONG.
+   *
+   * @param typeKind the TypeKind to inspect
+   * @return true if typeKind is a primitive integral type kind, excluding CHAR which does not print
+   *     as an integer
+   */
+  public static boolean isIntegralNumeric(TypeKind typeKind) {
+    switch (typeKind) {
+      case INT:
+      case SHORT:
+      case BYTE:
+      case LONG:
+        return true;
+      default:
+        return false;
+    }
+  }
+
   /**
    * Return true if the argument is one of FLOAT, DOUBLE.
    *
diff --git a/javacutil/src/main/java/org/checkerframework/javacutil/TypesUtils.java b/javacutil/src/main/java/org/checkerframework/javacutil/TypesUtils.java
index ccdc560e362..bd91c404e60 100644
--- a/javacutil/src/main/java/org/checkerframework/javacutil/TypesUtils.java
+++ b/javacutil/src/main/java/org/checkerframework/javacutil/TypesUtils.java
@@ -542,37 +542,40 @@ public static boolean isNumericBoxed(TypeMirror type) {
    * @return whether the argument is an integral primitive type
    */
   public static boolean isIntegralPrimitive(TypeMirror type) {
-    return isIntegralPrimitive(type.getKind());
+    return TypeKindUtils.isIntegral(type.getKind());
+  }
+
+  /**
+   * Return true if the argument TypeMirror is a (possibly boxed) integral type.
+   *
+   * @param type the type to inspect
+   * @return true if type is an integral type
+   */
+  public static boolean isIntegralPrimitiveOrBoxed(TypeMirror type) {
+    TypeKind kind = TypeKindUtils.primitiveOrBoxedToTypeKind(type);
+    return kind != null && TypeKindUtils.isIntegral(kind);
   }
 
   /**
    * Returns true iff the argument is an integral primitive type.
    *
-   * @param typeKind a type kind
+   * @param type a type
    * @return whether the argument is an integral primitive type
    */
-  public static boolean isIntegralPrimitive(TypeKind typeKind) {
-    switch (typeKind) {
-      case BYTE:
-      case CHAR:
-      case INT:
-      case LONG:
-      case SHORT:
-        return true;
-      default:
-        return false;
-    }
+  public static boolean isIntegralNumericPrimitive(TypeMirror type) {
+    return TypeKindUtils.isIntegralNumeric(type.getKind());
   }
 
   /**
-   * Return true if the argument TypeMirror is a (possibly boxed) integral type.
+   * Return true if the argument TypeMirror is a (possibly boxed) integral type, excluding char and
+   * Character which do not print as numbers.
    *
    * @param type the type to inspect
-   * @return true if type is an integral type
+   * @return true if type is an integral numeric type
    */
-  public static boolean isIntegralPrimitiveOrBoxed(TypeMirror type) {
+  public static boolean isIntegralNumericOrBoxed(TypeMirror type) {
     TypeKind kind = TypeKindUtils.primitiveOrBoxedToTypeKind(type);
-    return kind != null && TypeKindUtils.isIntegral(kind);
+    return kind != null && TypeKindUtils.isIntegralNumeric(kind);
   }
 
   /**