I've never seen a ring with the marks on the outside of the shank.
However, a little research showed that Eastern European rings around the turn of the 20th C had marks on the outside like yours.
This is a Russian piece (pre-Soviet Union).
I looked at some Russian, Polish, and Austro-Hungarian marks but didn't see anything close to yours.
Yours are weak and worn so its really hard to tell what it is. My thought was a crown over 18 - which is an old British mark used on pocket watches. I found no evidence of it used on rings or other jewelry.