Thank you guys !
NATO what? Its a War Department conventional symbol from 1942...
Historicaly the division symbol was re-used for Brigades, Squadrons and Companies with a unit number at the left (4 or D). In some manuals, a little abbreviation (Rcn, LT, HQ, Serv.)
Actually I use this one to indicate clearly the activitiy. In this case:
"reconnaissance and security missions, screen the advance of other tank units, etc."
But to avoid controversy, I can go back to the good old way.
Frankly, you shouldn't care of the previous remarks (too much "à coté de le plaque"). Your drawing are just superb and there is nothing to add nor remove nor change.