First, youre welcome, and I love your sticker idea.
I like comparisons. It quickly gives the comparison between the three in a simple way.
These examples are not intended as a comparison just how I typically think of the three;
Signal is first class mail - its delivered by someone who isnt going to read it in a sealed envelope. You can send stuff that cant in a text (better photo, a pdf doc, etc).
Whats app is a letter scanned in and emailed to you through gmail (like fbook almost everyone has a gmail) - its contents are visible to who delivered it, and its forever online in the database even if you delete the message or your account.
SMS is like a postcard - the carrier can be trusted to deliver the message, you dont know if anyone has read the message, and the carrier will take a picture of of the message and store it forever.
Keep doing your own thing… Its already pretty awesome as is.