If you want participants to identify marks, please show sharp close-ups of the marks
you want to know about. There is not a good idea to show three almost similar pictures of the marks from such a long distance you do. Look at the picture below. It is a picture copied and cropped from one of your pictures above. The quality is not so good but the distance is. With close-up pictures in focus similar like this you have a 100% better chance to get an answer otherwise it easily becomes a pie in the sky.
Anyway, the Greek letter behind the neck is of utmost importance. It looks like Greek alpha being the sign for St. Petersburg. Between 1912-1915 a master by the name of Gennady Konstantinovich Pavlov worked there. It could
be him. But again as in the other thread, let's wait for other opinions.