From left to right: second lieutenant Zbigniew Mieczkowski - cavalry captain Kazimierz Duda - lieutenant Michalski.
About the sign, from Robert Ostrycharz - Sikorski Polish Club (Glasgow) : The Division's Battle School also written in Polish as I think Division Training Centre. The number '40' is the vehicle marking for HQ 1 Pol Armoured Division plus you can make out the Division's emblem.