Is there a way to tell if brake fluid in a car is silicone or not?

[Gunslinger]

Does it really hurt anything if you do mix the two? I've done it and never had a problem.

Yes it is bad. The two types are not compatible. It will make a cloudy mess in the brake system and it can create clogs and you won't be able to bleed out the air. You won't get much pedal...it will be soft and spongy and take much longer to stop the car if it will stop at all.

There is also a DOT 5.1 fluid which is non-silicone and will mix with DOT 3 and 4. It's confusing with the different designations.

[StudeRich]

My method of telling Dot 3 from Dot 5 is easier, I just smell it!

Glycerin and Alcohol definitely has a distinctive odor.