There are a few selected buildings that are home to the special Glyphs that you can decode. Not that it is not a requirement to do them all, but if you want to Plat this game then you will be.
To scan a Glyph, all you do is hold the
button to activate Eagle Vision and then you approach a Glyph. Then you will have to figure out the code by solving a mini-puzzle/rhyme/riddle (whatever you would like to call it).
The easiest location of a Glyph is when you make it the Villa Auditore. Stand and face the front of the mansion. Hold
and look up and to the left. You will see the Glyph plastered on the outside wall. Simply climb up to it and then solve the puzzle.
I can't for sure say what puzzle you will get because none of the puzzle are specifically tied to a Glyph. The first few are fairly easy but they can be crazy difficult between your 15th and 20th Glyph.