Not only across Europe, they are more or less similar all over the world.
https://visual.ly/community/infographic/science/prehistoric-...
https://visual.ly/community/infographic/science/prehistoric-...
But meaning? I'm guessing something like "# was here".
If there are N number of confusing junctions, it would require the same number of markings as a unique mnemonic device to register the steps to escape the confusing area, and jog one's memory of how directions were negotiated the last time.
0 - All Time periods
1 - All Time Periods
# - All Time Periods
Please ensure your password contains at least one digit and one special character! Will we ever change?
PS There was also a null symbol.
X - All Time Periods
PPS Too bad they forgot to write comments, or we would know what all the symbols mean!
# - All Time Periods