diff --git a/ndn-cpp/data.hpp b/ndn-cpp/data.hpp
index 1f192b9..f8cc893 100644
--- a/ndn-cpp/data.hpp
+++ b/ndn-cpp/data.hpp
@@ -16,6 +16,7 @@
 
 /**
  * A Signature is an abstract base class providing methods to work with the signature information in a Data packet.
+ * You must create an object of a subclass, for example Sha256WithRsaSignature.
  */
 class Signature {
 public: