Coming late to the party and with >10 answers already, I still want to chip in because I did not see one aspect mentioned that I consider important.
What does make-up signal about you? Two things: Honesty and diligence.
Honesty first: Without make-up you show yourself as you are. Nothing is hidden, nothing is manipulated. This demonstrates that you are content with yourself and don't feel that you need to hide something. In a technical profession, you would be judged by your competence more than anything else, at least when more than a superficial first impression is concerned. Wearing make-up and showing gaps in your competence would make others judge you as shallow and fake.
This is different in professions where the first impression is very important. Sales and marketing would be obvious examples. In sales, your performance will be easy to measure, and if you are good you can get away without make-up. But it becomes worse in areas where the quality of your work is more subjective. Most people in marketing are not only good at selling a product but also at selling themselves. Here, make-up is more important if you want to look professional and will direct others to judge you more positively - looking like a wallflower will bias their judgement into a direction which will be hard to change later no matter how good your work is.
Now to diligence: If you put some effort into improving your looks, it reflects positively on your personality. Don't overdo it, though, and always be aware that your opinion and that of others has been heavily influenced by advertising. The massive amount of money spent on promoting essentially useless products does have consequences, at least subconsciously. The biggest make-up producers typically spend nearly 30% of revenues only on promoting their products. This will leave traces in peoples' minds - why else would so much money be spent each year?
But more important than your make-up will be your hairdo and your clothes. Messy hair and sloppy clothes will reflect poorly on your personality, more than not applying make-up will. If you wear clean and neat clothes, you don't need make-up to show that you take care in yourself and, by extension, in your work.
While a bit of eyeliner and mascara can help to enhance your eyes, too much can be overwhelming and unprofessional. A bit of eyeliner and mascara can enhance your eyes and make them look more awake and defined. Applying too much eyeliner and mascara can make your eyes look heavy and dark and make them appear smaller, which can be distracting and take away from the natural beauty of your eyes. Additionally, applying too much mascara can cause clumping and smudging, which can make your lashes look less defined and can create a messy look. This is inappropriate for a professional setting, as it can make you appear unkempt.