The French Army used playing card symbols to distinguish platoons and companies in world war 2.
Each platoon had its own symbol. The colour indicated the company.

Blue for no.1 Company.
White for no.2 Company.
Red for no.3 Company.

Spade symbol for the 1st platoon.
Heart symbol for the 2nd platoon.
Diamond for the 3rd platoon.
Clubs for the 4th platoon

(http://i283.photobucket.com/albums/kk307/minimischutter/th_13767229_306860889662520_8134812005676533504_o_zpswavebnui.jpg) (http://s283.photobucket.com/user/minimischutter/media/13767229_306860889662520_8134812005676533504_o_zpswavebnui.jpg.html)
Platoon identification symbols.

(http://i283.photobucket.com/albums/kk307/minimischutter/th_B1-bis_zps5vzjjmfh.jpg) (http://s283.photobucket.com/user/minimischutter/media/B1-bis_zps5vzjjmfh.jpg.html)
Example, a tank from 2nd platoon, 3rd company.

The Company commander has a symbol containing all four platoon symbols.

Source: Tankhunter FB