.... A triad of symbols.
No, it's the cross of St. James. Which was used by the order of Santiago.
https://en.wikipedia.org/wiki/Order_of_SantiagoA lot of these weren't answered so I'm putting the answers here.
McLovin and Nick Lazanis both have Greek soldiers as their avatars.
SamTheZamER's avatar is of German mounted troops.
seantheimpaler's avatar is from the Museum of The Royal Artillery.
Andee's avatar is Jean Lannes.
Nipplestockings' avatar is Caps for sale.
hardcorefreestyleboy's avatar is a drawing from the late 1800's.