Forgot to rsvp sign

I seen people do it where it’s an escort card like this:
https://i.pinimg.com/originals/8a/6e/d6/8a6ed6ca950f88b7a4fc427d0b6fd9d0.jpg

What Melle posted is something I’ve seen on Pinterest. I’ve never actually seen this is person though.

Wow, you are a lot more patient than I would be with those people! I would definitely call anyone who had not RSVP'd and (pleasantly) demand that they verbally RSVP.
If you're doing a seating chart instead of escort cards, you could have a box in the bottom right corner of the chart that says, "Don't see your name? If we didn't receive your response to our invitation, we didn't assign you a seat. It's okay though, we're still happy you're here. Get cozy and make some new friends by sitting right next to the other people at this table for [guests who didn't RSVP.]" You seen nice, so you may want a slightly less passive aggressive ending than the one I put in brackets, but hopefully that will help anyway.

Found these table cards that say "I Didn't RSVP but Came Anyways"

Does your caterer allow you to feed people you did not account for? I would double check with them before allowing non-RSVPers to have a seat.

WOW! I've actually never seen this option before. I might actually have to check with our venue to see if we can do this. If so, I'm stealing the table card idea lol.

Ha. My mom or sister will personally be calling people who have not RSVP'd and harassing them (ours is destination). There will be no unknowns at ours.