for me, i knew DD had dropped as i could quite literally feel her head butting on my cervix (sorry if TMI!). also, when i sat down too fast i would get a pang 'down there' (again, head butting my cervix lol!). another sign was the 'waddle' that became almost comical as again her head was really in the way...

she dropped at 35 weeks for me and arrived at 38 +2...