People around you will notice. As you train, more and more, your body will go through multiple obvious changes that you might not even be aware of. Keeping track of your own progress is important in order to stay fully motivated, to compare your gym programs, and to make you smile quite a bit. There are many ways of seeing your progress; here figure my favourites.
1 - Notepads and sketchbooks
If you're mathematical, or just like numbers when it comes to training, this is probably one of the best solutions. You can write on a notepad of any other piece of paper. I recommend writing how much you weight each Friday, how much you can lift, for how much time you can run, your best distances, your cheat meals, and your favourite exercises.
Then if you are really into statistics, you can even draw a plot and easily follow your progression.
2 - Selfies
Right? Taking selfies is still a lot taboo and really shouldn't. It's not about taking the selfie-- it's really about what you do with it. Personally, I take a mirror shot every Friday and put the files in a folder on my computer, labelling every picture with the date it was taken. Then you can pretty much get a good picture (pun!) of what's changed, and what's to be changed.
For example, if you notice that you crew pecs and a 6 pack, but still have the same legs, you know what to do.
3 - Post-its on your scale
If you have your own scale, it's fun to snap post-its on it. You can write your objectives and see yourself getting closer and closer. You could also write your progression on the post-its and try to beat you high-score every month. Really, it's all about beating your personal best score.
4 - Make it a ritual
In order to get unbiased results, you have to calculate your stuff in the exact same condition every time. If for instance you start a workout with deadlifts, and the week afterwards, you finish your workout with the same exercises, you'll probably be really disappointed. Same goes for the scale. You should always get on it after waking up, before eating, and especially if you always sleep with the same PJs (or naked) so you can get a clear idea.
5 - Meet up with old pals
"Giiirl, you've been working out? Wow, you look amazing!"