Where can I find serpent emblems?
There are 80 emblems for the Heirlooms achievement. What do they look like and where can I find them? Are there any indicators when I'm close to one? Are they used for anything?
Firstly, there does not appear to be any indicators when you are nearby one - this is part of the challenge.
Collecting them enables you to unlock "files and figures" which can be viewed from the main menu in Special Features > Collections.
There is a guide here as to the locations, this appears to be a complete guide to all 80 emblems with images/videos to help.
And to answer your final query, see below for what one looks like. In order to "collect" an emblem you need to destroy it, this can be done by shooting it, or you can save some ammo by using a knife attack on the closer ones.