A big sign may give the driver a crucial extra second to stop. The only canvas I usually have, however, is my notebook, so most of my signs are not big, bold, or beautiful. Then if the driver offers to go further, I have that choice. On the other hand if you go for the whole shebang, you just might get it. Another trick is to use the native spelling of a city, such as K benhavn for Copenhagen, Athina for Athens, Twitsville for Paris, etc.
Many drivers naturally prefer riders who speak their native language.
A border makes the sign stand out. Look like you have somewhere to go, and that you really want a ride. For interesting reading check the light posts and road signs where hitchhikers traditionally ply their craft. Scrawled there will likely be a poem or message to you, the future hitcher, from some rhapsodic or desperate soul from long ago. Hitchhikers exude inspiration, and there is nothing between you and it but time.