SQL Server - How to know to which database user certificate is mapped to?

Question

Inside a user database, I have two certificates, both are used for signing stored procedures

First cert was created long time ago by someone
Second I created myself for testing purposes

For second cert I also created database user from certificate

When I query sys.certificates, I can see column [sid]

For the second cert I can find this [sid] in the sys.database_principals and can see which database user second cert is mapped to (which is the user I created)

When I do the same for first cert (created by someone long time ago),
this cert's [sid] can't be found in the sys.database_principals

Question: how do I find out which database user first cert is mapped to ?