Here's a link to my website for some info: http://www.panchogun.com/FVWebPhotos/FV-Beretta-4UT-5x100px.jpg
And here's some additional info:
1. Jan C. Still, in Axis Pistols, page 107, states, "It is likely that almost all of the 4/UT, ...were used by the German Army". He also includes two other variations in this statement, "1944 dated and blank slide Model 1935".
2. Ugo Menchini, in Pietro Beretta Le Automatiche, page 326, states, "After the 8 September 1943 armistice between Italy and the Allies, the Germans saddled Beretta with three engineers from Germany. Moreover the factory was garrisoned by the SS... Weapons of that time, even the ones produced for the Germans, bore the punch mark 4UT (Quarto Ufficio tecnico di Controllo Armi e Munizioni--4th Technnical Control Unit), impressed prior to d[e]spatch to purchasers."
3. Ugo Menchini, in Pietro Beretta Le Automatiche, regarding an M1934, page 255, states, "In late 1940 there appears an oval including the punch mark IVU. It refers to the 4th technical Control Unit of the ***, where inspection was carried out."
4. Note that, while they seem to represent the same inspectors, the "IVU" is not the same mark as the "4UT". The IVU would be found on the pre RSI model M1934, and the 4UT would be found on the RSI model M1935.