The best way would be asking people on the streets no?
not convenient and practical at all
I think that price is the best way. If moon, it means people are excited, if dump, it means people like fiat more than btc.
could be manipulation, not a good option
i think th best solution is by looking at the number of transaction per day, those that are "cold storaging" will end their work at the end so if the number of TX per day rise, it must be because new people joined in