In Tiberian Sun and Firestorm
The rules.ini description suggests, it was supposed to make the unit able to steal credits just like the Thief in Red Alert. Unfortunately, the flag does nothing at all.flag was introduced in Tiberian Sun, and as its name and
In Red Alert 2 and Yuri's Revenge
allows the infantry to enter a refinery when used with in RA2 but it does not steal any money. For the same in YR, the infantry is rejected from entering, so it cannot enter the buildings. Stealing credits is now achieved by using in RA2/YR.
is also required for to work correctly. Yuri's Revenge at least, if is set on an InfantryType then that InfantryType will be unable to enter guard mode. For example, setting on an Attack Dog will prevent the Attack Dog from detecting and attacking disguised enemy units automatically.