Need Help With This Russian Stamp ( Small Cyrillic F Or?)

I decided to investigate my collection, I bought a long time ago and found this purchased as SC# C68b stamp with a supposed Cyrillic small F. But looking at the stamp I am not so sure that it's a small F.

Can anyone please confirm or deny?
Also,can someone explain the difference between a vertical or horziontal watermark on said stamp?

If anyone knows what would today value be estimated at?







With respect,

Your stamp is not a small "f" variety. Below are my C68 and C68B that were recently sold at auction by Raritan. The C68, MNH realized $400 and the C68B, MLH realized $400 as well. I cannot tell from your back image what the condition of the gum is but I do see the appropriate expertizing and authenticity marks.

C68


C68B

Thank you so much for your reply! I thought so. Hope you have a good day.