If it truly is 50 mW, it will be dangerous for your eyes. Looking at the dot on a non or barely reflective surface (walls, carpet, wood, etc.) should not be harmful. However, although diffuse reflections such as those are not dangerous, any accidental direct reflection off of things like mirrors, unpainted metal, silverware / glass cups pose a substantial threat.
If you STRICTLY follow rules such as; don't point the laser anywhere near reflective surfaces or people you will probably not need safety glasses. I highly recommend them however, because an accident can always happen, and safety glasses can mean the difference between two remaining eyes and one.
Use a sharpie or similar black marker to color a blown up balloon. Shine the laser at the dark spot and see if it pops. This is a very rough estimate, but if it can pop the balloon then it should be at least 40 mW+. Then try smoking black tape, which should test it at a minimum of 60~ mW. Remember, this is a VERY rough estimate due to other factors affecting the burning capability such as the size of the point (power over area), and different types of tape / balloons.