Hi Massimo,
This acronym stands for UTI-3, Ути - 3 in printed cyrillic , and
in italic cursive . The T turns into M. I was able to reproduce it on hand made decal. I was unable to understand the 3 signs on the star, so I reproduced them as I saw.
The cowlings of both planes are NACA and this changes the aspect of the planes . For the I-16 V, I used the drawing of Maslov and the cowling has the same length than the ICM, 15 mm For the UTI-3, I used the side picture and the cowling is longer, 17mm.
Regards
Bernard