Signs you think about leaving your current job:
- The company culture has changed in ways you don't like or recognize
- You are no longer proud of the work you do
- You are always feeling tired, even when you just got to work
- You more easily notice your coworkers' screwups and are more easily annoyed at them
- You feel unappreciated for the work you do
- You feel like the company doesn't listen to your inputs
- Many of your close friends in the company are unhappy and want to leave or are already leaving or have already left
- You no longer trust your boss to make good decisions about the company's future
- You are always looking for more free time to pursue other pursuits
- It's Monday and you're already looking forward to Friday
- You hate your commute
- You start reading articles about signs you should think about leaving your job
A lot of people feel trapped in their current job. They feel that they will be unable to find better or at least similar work and will rather stay than risk it. It's a false sense of "job security" vs fear. It might be true that you have no good options. But if you're not looking at all, it's 100% surely true.
Even if you don't find better options, the act of looking for them helps you through some sort of catharsis. It confirms if you really have no choice but to stay. It helps you understand your place in the job market and what you can do to improve your position and maybe open up more options later on.
Bottom line: if you're unhappy in any way (as indicated by any of the signs above), you should at least be looking. Otherwise you are doing yourself a disservice.