How do I seal chalk paint without it smudging?

I use a wax to seal my chalk paint.

Wax for chalk paint or it will smudge. Otherwise change paint.

I would use a different paint.

whats the best paint

If the paint is dry, sealing it with clear wax shouldn't give you any problems. You don't need a super tough protection for signs, since they are not high-traffic pieces like tables or chairs. If you choose to try a different paint, I suggest General Finishes milk paint, or Fusion Mineral Paint. You won't need to seal your signs if you work with those. Good luck!

How soon are you sealing? I recommend waiting over night before sealing. Otherwise yes-spraying first can help but shouldn't be needed. Wise Owl Products are my favorite... I do signs and they turn out great-no smudging https://www.thatsweettealife.com/store/

I imagine no one other than you would know what type of paint you're using, therefore using chalk paint is not critical I'm guessing -- save yourself the extra steps, extended time, effort, and expense and use a different type of paint.

It sounds like you're not letting the paint dry long enough. I've never had chalk paint smudge. Unless you're talking about chalk paste like Chalk Couture or A Maker's Studio. Then spray it first with clear spray paint.