There is no UI to tell if a clip has a frame hold applied to it or not on the timeline. This isn't really an issue with live action moving footage, it's usually pretty apaprent, but when editing screen recordings and the like where you may have extended a moment by adding a frame hold, it can be hard to tell what is going on with the underlying footage when you come back to the edit sometime later.
The only way I've found to check if there is a frame hold is to enable overlays and look and see if the timecode changes over a clip.
Proposal:
Add an icon or text to indicate when a clip has a frame hold applied to it.