I don't know if it would make a difference in which part of the world you find a sign, as to what it would mean, but it seems to me that different cultures having different beliefs as to what was sacred would make a difference in the types of symbols they would use for treasure sign.
Not being specific about the "country" could be a disadvantage to some of the folks here who would best be able to help you. If you don't give specifics (what map you used or what city is nearby) your find should be safe. However, I personally think a geographical area would help immensely.
One question about the turtle . . . was that plaster looking stuff covering the whole turtle at one time?