Consider the shop code on the left side rail. Some are pretty rare and much sought after. Things like VR69, TR137, радионица (Radionica) 124” and радионица (Radionica) 145. TRZ.5 in italic script font is common but in straight font less so and even rarer are TRZ-5 (specifically with the hyphen).
Below are a some examples of markings to look for.
Attachment 76392 Attachment 76393 Attachment 76394
Attachment 76390 Attachment 76391