diff --git a/book/source/19-zoom_signatures.md b/book/source/19-zoom_signatures.md
index f384ef4..8118896 100644
--- a/book/source/19-zoom_signatures.md
+++ b/book/source/19-zoom_signatures.md
@@ -169,6 +169,7 @@ Signature Packet, new CTB, 2 header bytes + 152 bytes
     00000090  f5 e0 58 cb ae 9a ff 7a  a4 05
 ```
 
+(cleartext)=
 ## Cleartext signature
 
 ```text