I'm the original poster.
Thanks to all for the good advice.
I went to Lowe's this afternoon and bought some Tapcons. I wanted 3/16 x 3 1/4" but they didn't have that size so I went up to 1/4" plus the appropriate bit.
It's on the wall now and is very sturdy. Wy wife is delighted which I expect you can all appreciate is a good thing.

In case you want to see the artsy New Orleans-themed sign that our son made for her, I uploaded a pic to Google drive:
https://drive.google.com/file/d/1fMK...ew?usp=sharing

Can a file be attached to a post in this newsgroup?
Bob Simon