A number of soviet vehicles have this tag but I don't see any explanation as to what it does.
My presumption is that the ATGW in question cannot be fired as part of a move and shoot with stabilisers?
No ATGW can be fired with a Move/Shoot action.
All ATGW must be fired whilst the shooting unit is stationary (well, there are exceptions in the case of later 'Fire & Forget' type technology, specifically for helicopters, but that's a different matter).
The designation in the list is purely to remind players that this particular weapon type (which in this case is fired via the same barrel as the conventional AT rounds) cannot be fired if the unit has moved or plans to move in the same turn.
Cheers
Mark