Like the title says, when do you see the true bear market that we saw that happened in 2018 with every alt crashing insane amount?
If bitcoin crashes for about a week or so and then most altcoins are following the downtrend, without any signs of any upwards movement nor indicators doesn't show us that price will rise soon, I considered that as the bear market is now in effect.
But honestly, you don't need any signs to know that the same scenario in 2018 will happened again. Just focus on the progress made by bitcoin after that 2018 bear trend and form an analysis if the same case will happen again and some possible factors that might trigger it.