diff --git a/book/source/06-signatures.md b/book/source/06-signatures.md
index fb8dc51..f8c16f7 100644
--- a/book/source/06-signatures.md
+++ b/book/source/06-signatures.md
@@ -27,6 +27,7 @@ show our visuals for these two layers of meaning?
 - box with yellow tag-thing, including sig-circle
 ```
 
+(signature_types)=
 ## Types of signatures in OpenPGP
 
 The OpenPGP standard defines a set of [Signature Types](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-12.html#name-signature-types), each identified by a numerical *signature type ID*. Signature types define the intent of a signature, and how it needs to be interpreted.