"What is the best way to tell (without a hydrometer) if fermentation has stopped?"
As others have recommended, bottle 3 weeks from starting.
Right, wrong or indifferent, all my brews are bottled at 3 weeks.
After 3 weeks, then carb/condition for an additional 3 weeks @73F, then stored @60F.
Beers are chilled for 2-3 days in fridge when ready for consumption.
Honestly, I forget about the brews until my calendar says to brew, bottle, or ready.
Haven't bought beer for about a year, and I have 2 with dinner every night. Currently
drinking a batch, 2 other batches are drink ready, 1 batch in 3 week bottle condition/carb
phase, 2 batchs fermenting, one of them will be bottled tomorrow.
About every 2 1/2 - 3 weeks a new batch is brewed.
I recommend for some time to only focus on procedures, malts, hops, and yeasts,
adding nothing else to the beer.