Is this spider mites sign?

Well, you can't actually SEE them yet - but you will! That's the first sign of thrips... there are several things you can do but you need to make a choice and do it FAST because those little buggers will ruin everything. You can try sprinkling some diatomaceous earth kind of all over the plant and on the soil ... this is organic and some folks actually eat the stuff (don't ask me why)... but it will kill pretty much any insect that comes in contact with it within 24-48 hours... might kill thrips inside of 12 hours since they're so small... it works by dessicating them. The downside to this is it would need to be reapplied when it gets wet. Second option is to spray some Neem oil on both sides of each leaf. This is also an organic but very effective solution. Biggest thing here is to act fast.... and then stay vigilant! I would say you should repeat whatever treatment you choose at least once a week for a couple of weeks at least. Another good thing to do is to clear out your tent (or grow room or wherever these ladies are), clean out any dead leaves/etc and wash it down with 1tsp hydrogen peroxide per gallon of water. If your pots are ceramic, wipe them down as well, if they're fabric, you can spray them with the solution. Thrips are hard to get rid of... but you've caught them early and that's nothing but great news....