If coolant is being consumed by the engine, eventually, you'll see a drop in the reservoir level. Keep your eye on it. Of course, as the temps drop, the exhaust system becomes just a big condenser - and since H2O is one of the primary products of combustion, we'll all see tons of vapor out the exhaust until the system warms up enough so that the condensation doesn't occur. The telltale is the antifreeze smell -- if you've got a blown head gasket or a cracked head so that coolant is entering the chamber - and enough vapor is present to show "white smoke" when it's warm outside, you'll smell the antifreeze.

I once had a '67 Datsun RL411 (preceded the 510) that would show big clouds of vapor/antifreeze smell on start up. Once the engine had been revved a few times (30-60 seconds) it would all go away. Over time I noticed some fluid level dropping under the radiator cap. Turns out the head was barely cracked in one of the chambers. When the engine was cold, the crack would open up enough to allow a bit of coolant to leak into the chamber. So as the car cooled down overnight, a bit of fluid would sit on top of the piston. When I'd crank it up -- it would steam that out through the exhaust. As soon as the head got just a touch of heat in it, expansion would close up the crack --- ran perfectly with no fluid loss. Shut it down for the night and it would all start over again the next morning. Hard to diagnose. Pulled the head thinking it was the gasket. Had the valves redone while I had the head off -- the machine shop found the crack. I asked them to check -- couldn't see it with the naked eye, and the head gasket was fine. Go figure.
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82 242-6.2L; '17 Mazda3; '16 Crosstrek