Yes those are the signs of the start of flowering but about the topping method topping is for the veg growth wouldnt do no good in the flowering stage and could put stress on your plant. In your next grow that is when you should test out topping and other methods O and dont forget to start your flowering nutrients on NPK you need more P (phosphorus) and little N (nitrogen) and K (potasium) i would keep that the same.Also 2 weeks before you chop it down give it no more nutrients and start flushing wich is the prossec of watering your plants more and draining the exess. this will clean the plant of any toxin and give you a more cleaner and tasteier smoke. PS flushing will make the leafs start to turn yellow and fall off dont worrie this is natural. just let them fall off dont clip them....Hope this helps with the flowering stage Good luck!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!