diff --git a/iscc_core/constants.py b/iscc_core/constants.py
index afb73ee..7a221d2 100644
--- a/iscc_core/constants.py
+++ b/iscc_core/constants.py
@@ -18,6 +18,7 @@
 IsccTuple = Tuple[MainType, SubType, Version, Length, bytes]
 IsccAny = Union[str, IsccTuple, bytes, "Code"]
 Properties = Union[dict, bytes]
+FrameSig = Tuple[int]
 
 
 class MT(enum.IntEnum):