You can unlock this as early as DNA Sequence 2. Glyphs are markings located on the walls of landmark buildings. As locations are added to your database, some entries will have a icon in the top left corner, signifying that this location has a glyph somewhere on it. There are 20 in all located in the five cities. They glow white so are visible to the naked eye. When you find one, stand (or hang) in front of it and hold to activate your Eagle Vision, thus unlocking this achievement.
The first glyph available is at the top of La Rosa Colta, the building where you agree to meet Annetta at (to start the memory ‘Fitting In’ in DNA Sequence 2). Refer to “A Piece of the Puzzle” for more information.
Refer to “Vitruvian Man” for a video showing the locations and puzzle solutions for all 20 glyphs.