Look at my signature, of the FotRSU splash screen shot, which is from cdrsubron7. There is the number "400" on the jull, for the Balao Class Sea Devil boat. I asked him years ago - prior to my 'propbeanie' name (long-lost original name forever gone into the depths of grey matter), and probably his being over at the Ubisoft forums where he was a mod at the time - how he had numbers on the hull, and he pointed me to the mod, probably the one your are referring to MM. From what I remember, it was like the Kill Flags roll-your-own kit in that the user input his own number, which was then loaded as a mini-mod through JSGME - possibly...
The computer in the corner KM, is thus far not divulging any "secrets"... but it seems to me that there was a node on either side of the boat, and the ambient occlusion was used for the number - but don't take my word for that... I mean, after all, I did point you all to a "numbers" mod... just not anywhere near the correct one...