For repository maintainers seeing issues and pull requests sent from first-time users, sending some happy "thank you!"s and emojis to the users can be a very encouraging, inclusive behavior. For example: https://github.com/DefinitelyTyped/DefinitelyTyped/pull/25007#issuecomment-381767908
Here is what GitHub shows for first-time users on their first pull requests:

...which is easy to miss and doesn't give much indication that this is a good time to encourage the user.
We already have ๐ suggestions from GitHub on the user's side:

How about adding versions of this for the maintainers' side?
"๐ / It looks like this is
"๐ / It looks like this is
Mockup:

_(instigating Twitter thread: https://twitter.com/JoshuaKGoldberg/status/1019260761569280000)_
You could make a link in that popup on the maintainer's side to automatically populate the comment field with a message thanking them for their contribution that you then add feedback to.

I like @jamiebuilds' suggestion, but I would randomize the emoji and text from a list of alternatives so it doesn't look machine generated. PR welcome.
For anyone that wants this, please also send this feature request to GitHub: [email protected]
Here's the documentation for that popover: https://styleguide.github.com/primer/components/popover/
I think this is a bit out of Refined GitHub's scope and its code would have to run forever even though it shouldn't be visible more often than twice a year or so.
I'd say GitHub should do this. cc @lukehefson
I'd say GitHub should do this. cc @lukehefson
Thanks @bfred-it โ I'll be sure to let the right folk/team know your thoughts!