The CR (X) spacing is irregular, so I was thinking it may not be a letter, but a number--like '8'.
Are there any marks on the reverse side?
The English word for 'armes' in French is 'arm' which made me think this is a French buckle designating the branches of military service--somehow.
Don........
Is the first button pewter or hard rubber? It looks like it might be one piece because of the chips on the side. The second and 4th I believe are civilian blazer buttons and the 3rd is a US army great seal button probably post WWII. the buckle I have no idea on.