I usually reply to their greeting-only message by reacting with a wave emoji.

It shows them that I've seen their message, but I won't be responding with my own message in order to pull a request out of them.

I'll occasionally end up with people creating tickets or making noise with managers if they're ignored. The only reason I stopped doing this, really.

Tickets are good. They give you tangible credit for your time spent helping someone. If they are interrupting your manager the same way they interrupted you, instead of sending a request in an efficient manner, they saved you the trouble of you going to your manager to ask for help dealing with the person being a nuisance.

In what world do tickets go to managers?

I wonder if if the integration hooks in slack have enough options to allow a good bot to help with this. I know they can identify and respond, but if they can't alter the message or noise it makes, maybe they can at least set a specific noise for the automated reply? Then if you recognize the telltale combination of the two, you can assume that initial interaction has been handled and wait until you hear the singular message received noise.

Last I had checked most platforms don't have much in the way of modifying messages or accessing PM/DMs.

What I wanted it for was a timezone converter, so everyone saw the time in their own timezone. Our group is from across NA, so somebody saying "I'll be on at 6!" can be hard to figure out when dealing with a dozen people from 4 timezones

Someone needs to write a Slack extension (or whatever the plugins are called) that simply replies to "hi" or "hello" with "Hello! How can I help you?" and hides those opening salvos from you.