Alcatraz - Block C - Federal Penetentiary Key Chain

Hi,

I was wondering if someone with a lot more knowledge on this sort of stuff could help me identfiy if this is a souvenir from Alcatraz or an original key chain from the prison.

Wording is as follows:

Alcatraz

Federal Penetenciary

Cell Block C

San Fransico

Looks quite an old item and has unusual markings on the reverse.  Its quite heavy as well.

Hopefully me pictures do it justice and somebody can help me out.

Fair