diff --git a/masque/label.py b/masque/label.py
index 738ab20..2a2b56d 100644
--- a/masque/label.py
+++ b/masque/label.py
@@ -24,6 +24,9 @@ class Label:
     # Label string
     _string = None                      # type: str
 
+    # Arbitrary identifier tuple
+    identifier: Tuple
+
     # ---- Properties
     # offset property
     @property
@@ -76,6 +79,7 @@ class Label:
                  string: str,
                  offset: vector2=(0.0, 0.0),
                  layer: int=0):
+        self.identifier = ()
         self.string = string
         self.offset = numpy.array(offset, dtype=float)
         self.layer = layer
diff --git a/masque/repetition.py b/masque/repetition.py
index efa91a7..8618ba6 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -3,7 +3,7 @@
      instances of a Pattern in the same parent Pattern.
 """
 
-from typing import Union, List, Dict
+from typing import Union, List, Dict, Tuple
 import copy
 
 import numpy
@@ -37,6 +37,8 @@ class GridRepetition:
     a_count = None          # type: int
     b_count = 1             # type: int
 
+    identifier: Tuple
+
     def __init__(self,
                  pattern: 'Pattern',
                  a_vector: numpy.ndarray,
@@ -77,6 +79,7 @@ class GridRepetition:
         self.a_count = a_count
         self.b_count = b_count
 
+        self.identifier = ()
         self.pattern = pattern
         self.offset = offset
         self.rotation = rotation
diff --git a/masque/subpattern.py b/masque/subpattern.py
index 88fe2ee..c84305c 100644
--- a/masque/subpattern.py
+++ b/masque/subpattern.py
@@ -3,7 +3,7 @@
   offset, rotation, scaling, and other such properties to the reference.
 """
 
-from typing import Union, List, Dict
+from typing import Union, List, Dict, Tuple
 import copy
 
 import numpy
@@ -28,6 +28,7 @@ class SubPattern:
     _dose = 1.0             # type: float
     _scale = 1.0            # type: float
     _mirrored = None        # type: List[bool]
+    identifier: Tuple
 
     def __init__(self,
                  pattern: 'Pattern',
@@ -36,6 +37,7 @@ class SubPattern:
                  mirrored: List[bool]=None,
                  dose: float=1.0,
                  scale: float=1.0):
+        self.identifier = ()
         self.pattern = pattern
         self.offset = offset
         self.rotation = rotation