Feature Request - Rules Integration - Configurable Message

We have a lost pet web site and people often look for pets, without registering their own pet.

It would be great if a Rule could be set up so that when someone checks the listing, a message pops up asking if they have registered.

I am not currently using the module but it appears it is for Drupal system messages, and I can't tell if configurable messages can be used.

I do not think there is currently any module which provides a "configurable message pop up" function. Thank you.