Going through some things left to me by a relative, I found a box containing a kind of stone stamp press and a letter explaining that it was found in the 80s at the Temple of the Feathered Serpent at Teotihuacán. The letter says that the stamp is 12th century CE and that it was used by Aztec Jaguar knights to indicate their identity when not wearing their cloaks. I would like to find out if the thing actually is what the letters claims it is but I have no idea how to do that. Apologies if this not the appropriate sub for this question.
I find this sub to be a great resource and I always enjoy reading the thorough and enlightening content the historians provide here. You may also consider cross-posting to r/anthropology r/archaeology or r/archeology . They may be able to provide resources more specific to physical anthropology as well as information pertaining to descendant groups for more insight or to potentially repatriate the artifacts. What a fascinating journey this could be and I wish you luck in your search.
If the item is really from the 12th century and found in Teotihuacán then it is not, by definition, Aztec. Teotihuacán had its own civilazation (its exact ethnic identitity is still debated) and was a vast multicultural city so the artefact could be any number of cultures such as Maya (if you need it to be from a sexy well known mesoamerican culture!) but not Aztec, they are a more recent culture than that. But really, who identified it in the first place?
If you are looking for expert identification, I would contact the Instituto Nacional de Antropología e Historia.
Of course if it is actually a genuine artefact of value and not a tourist scam or whatnot, then these are people who might want to reclaim it to preserve mexican heritage.
Are you writing from mexico or did this supposed artifact leave the country? 'Cause there's been laws against taking such things out of the coutry since at least the 70s, just so you know.
Trying to authenticate this object yourself would not be easy and likely not accurate. I would look up universities in your area with anthropology departments and see if any have an archaeologist who specializes in the Aztec period. Not all will, so it may take some searching. Take well lit photos of the object with some sort of scale (something like a pencil or pen would work if you don't have a ruler) and the letter. You should be able to email the photos to the archaeologist you have found explaining the circumstances and asking for help authenticating the object. Make sure to indicate it is something you inherited and are looking to see if it is authentic to figure out what to do with it because archaeologists are likely to be suspicious of artifact trafficking and looters. Honestly, it is very likely the artifact, if authentic, was brought into the country illegally if found in the 1980s and you don't live in Mexico. Even if you live in Mexico, there is a good chance it was sold illegally. You'd probably be better off legally and morally if it is an imitation. Not everyone will reply, both due to time constraints and due to the possibly illegality of the object, so it might be a good idea to email a few different people.
Source: I'm an archaeology grad student at a university who has received many such emails and social media messages requesting artifact identifications. However, I do not do anything at all related to the Aztec period so can't help here specifically.