What were the signs for me: No joy in life, even with hobbies or parts of works that were always pretty pleasant. Being snippy, dreading work days rather than having a neutral-to-slightly-positive take on them. (You don't have to always "like" work but I've found there's a real difference between dread and neutral).
When is it time to change jobs: When you really dislike the person you're becoming (irritable, unusually cynical) and don't want it to be permanent.
I got lucky in that (through higher-up corporate politics) I was accidentally(?) reassigned to something else much more joyful and fitting my skills quickly after I started noticing these signs, but it was absolutely a learning moment to see the shift in mindset and mood. This last comment may sound odd, but something I wish I did earlier was to start journaling as it's a great way to notice emotional patterns and to suss out things that have been bothering you but might not be vocalizing (as much as you need to).
When is it time to change jobs: When you really dislike the person you're becoming (irritable, unusually cynical) and don't want it to be permanent.
I got lucky in that (through higher-up corporate politics) I was accidentally(?) reassigned to something else much more joyful and fitting my skills quickly after I started noticing these signs, but it was absolutely a learning moment to see the shift in mindset and mood. This last comment may sound odd, but something I wish I did earlier was to start journaling as it's a great way to notice emotional patterns and to suss out things that have been bothering you but might not be vocalizing (as much as you need to).