What does "head the bill" mean?

Solution 1:

It's usually top the bill (bill = billing = billboard = a flat surface or board, usually outdoors, on which large advertisements or notices are posted.

To top the billing literally means to be listed at the top of the advertising posters (as the most important of several attractions), but it can be used figuratively. Note that in some contexts (bands at a concert, actors in a movie, etc.) the alternative sequence order of appearance may used instead of importance. Rarely, you may come across head the bill (but not, I think, top the bill) to mean be listed first in the promotional material because you're the first act to go on stage.

Solution 2:

If you don't head the bill you are not the featured performer ( in a promotion sense)!