Inspired by this question: Messi signed Barcelona jersey real or fake?
In the aforementioned question, the OP is unsure whether his autographed Messi jersey is real or fake. The only tangible bits of information that was provided is that the signature is slightly faded and came with a certificate from a website. Without more information about the seller, the website, and/or the legitimacy of the certificate, it is hard to decipher whether or not the signature is real or fake.
How can I verify the authenticity of my sports collectibles? Are there tangible ways in which I can verify my sports collectibles, whether through the items I have received upon purchase (eg, certificate of authenticity), through a credible verification service, etc.?