diff --git a/book/source/06-signatures.md b/book/source/06-signatures.md
index 7dc8b2f..0ba31e5 100644
--- a/book/source/06-signatures.md
+++ b/book/source/06-signatures.md
@@ -66,6 +66,11 @@ As outlined above, an {term}`OpenPGP signature<OpenPGP Signature Packet>` is a c
 Structure of an {term}`OpenPGP signature packet`
 ```
 
+The input data packets differ between specific signature types. Also see {numref}`fig-signature-types`. For example:
+
+- for a [*binary data signature*](data_signature_types), the input data packet is a *literal data packet*, while
+- for a [*subkey binding signature*](bind_subkey), the input data packets consist of a primary and a subkey packet.
+
 ### Creating an OpenPGP signature packet
 
 Creating an {term}`OpenPGP signature packet` involves encoding a statement about a specific set of data within the {term}`packet`.