Well if you saw it on your own phone just pull down the notification slide and you can see what app has produced it. Tap on it and it will open the app.
If what you actually mean is you saw it on an image from someone else, then frankly it could be anything. It could be a dating app, but there are many different types of app that use hearts or stars in their notifications, so it's best not to jump to conclusions.
My D-Bag (EX)boyfriend just flipped out at me over this icon, accusing me of nonsense about having dating app profiles..
It's ACTUALLY the icon for Rewarded Play. It's one of the multitudes of gaming apps that are currently being advertised EVERYWHERE, that give you points for usage time, that you can then trade in for various gift cards.
But hey, if you wanna get single fast, jumping to conclusions and making accusations is a good way to do it!