Is there a good standard?

It's very common to simply end with 1;. It's needed, because perl uses the last expression that was evaluated to determine if the module was loaded correctly. When it's not there, but the module still works, that means the last expression was true, but it's considered bad style to depend on that.

I've also seen people use strings over there (q/Murphy's law is recursive. Washing your car to make it rain doesn't work./;), or 42;, and other values representing truth.

44696420796F7520732F2F2F65206F
7220756E7061636B3F202F6D736720
6D6521203A29202D2D204A75657264