You should always take a gravity reading of your must BEFORE you pitch your yeast. Then, subsequent gravity readings will tell you if your wine if fermenting. You may also see some physical activity, but you can't count on that to tell you what's really going on.
Even if you miss the initial gravity reading, take one now. Then take one in a few days. If the second reading is lower than the first, your wine is fermenting. If it is at or below 1.000, you are just about done with fermentation.
If it is fizzing, it is fermenting.
If you can see bubbles escaping from the airlock, it is fermenting.
The problem starts when you do not hear fizzing anymore. Then it could still be fermenting but the rate can be so slow that you will not notice it.
Same goes for bubbling in the airlock.
One bubble a week is slow, but still fermenting.
An airlock is the best way (besides taking a hydrometer reading each time, which in my opinion is a waste of time) to see if fermentation is going on.
NOT bubbling does not mean that the wine is ready.
It only tells you that fermentation has stopped, which is an entirely different thing.