What is this character? How to identify it?
The character is the Shuowen seal form of「克」.

「克」was originally a compound of「由」(a helmet, top part of「冑」) and a reduced form of「皮」(an animal being skinned for its hide, with the action being represented by the hand「又」;「又」is not present in the original forms of「克」):



Illustrative purposes only; this may not be strictly how the character changed over the years.

Compare: