Report it if it's bothering you.

https://support.na.square-enix.com/f...&la=1&ret=rule

"Offensive expression" means an expression in general that inflicts emotional distress by being offensive to another person.

It is prohibited to do this anywhere an expression can be made, such as all chat channels (including PvP Quick Chat, macros, and emotes), markers, comments, or titles. It is also a violation in cases where a player character name involves a term that could be considered offensive in any way.
Logs will tell the GMs which player placed the markers.

As others have said, you can also remove them either by binding "Clear Waymarks" to a hotbar or by typing /waymark off

To those defending the placement of obscene phrases in game via markers or other methods - it's a nuisance behavior. Stop enabling social idiocy.