Most illegal services commonly go out of view behind a players shoulder or body.

A rule stating "the front of the server's shirt must be visible to the receiver" should fix the most common illegal serves.

It should be also very easy for the umpire to enforce, since they just have to look at which way the server's body is facing.

Maybe the rule's wording can be changed a bit ( "both shoulders" instead of "shirt", "facing the table" instead of "visible to the receiver" ), but the idea is still there.

What do you guys think?