There was a huge uproar when news that a visitor made an addition to the wall carvings in an ancient temple in Luxor, Egypt. The carved words are in Chinese and say "Ding Jin-hao (probably the engraver's name) is here for a visit". The engraver's parents have apologized on his behalf, but, given that the carving consisted of seven Chinese characters, meaning the engraving cannot be completed quickly, one has to wonder if the parents did anything to stop him.
The above is an extreme case, but it seems that a lot of people are very eager to let the world know where they have been to — scribbings have been spotted on rocks, trees, even on the Great Wall. Most of the writings consist simply of the writer's name (some also include the date they left their mark). Two names surrounding by a heart and/or connected by a +/& sign is the second-most common type. I've also seen writings/carvings which appear to be insults of attacks on certain individuals/groups (many of which are unfit to print).
For some people, carving one's name while visiting a place appears to be the preferred way of showing others the places they have visited. Do they leave a mark so that, should they make another visit to the place, they can recognize their favourite spot of the place? Do they carve their names onto walls/rocks so that future visitors to place know the engraver once visited there? Are they doing it for bragging rights? Are the engravers worried that they would be forgotten after they are gone? Are they trying to let archeologists of the distant future see what people in the 20th/21st century are like? The problem is none of the above is a convincing reason for defacing walls/rocks. One can show others the places they have been to by uploading pictures/videos to sharing web sites and brag to others by sending them links to pictures/video they posted. As for the last two reasons, one probably preferred to be remembered as more than someone who defaces nature/monuments from further back. (I am sure there are other "justifications" — the above are the only ones I can think of.)
It seems that, for some couples, one of the better ways to show their love towards each other is to carve their names onto rocks or trees. Perhaps they wish their relationship to be as solid as the rocks they carve on, or as long-lasting as the trees on which they leave their carvings. The problem is what would happen if the relationship turns bad. It is possible that one or both side, out of dejection, hatred, or other reasons, deface the name of their (former) lover or cover the name with their present other half. Leave the rock/tree out of the fight, it is innocent.
As for carvings meant for attacking others, one has to wonder whether they reach their intended target at all. While the those making the scribbing may wish to get the people who read their message to agree with their views, it is doubtful After all, who would be swayed by random markings on rocks, lampposts, or bus signs? (If such people exist, they can easily be swayed by another side.) Besides, very few, if any, passers-by would pay any attention to the message at all. (I guess I am one of the few who even glance at them.)
There are plenty of ways to show the world where one's been to, who is in love with whom, and to broadcast one's message today — sharing web sites, photograhs, even home-made publications. So one has to wonder why people still do the above using a method from the stone age.