If you notice that your vehicle starts to drift to one side slightly, even when on a flat straight surface, this is one sign that the alignment may be out.
Off-centre steering wheel
Stop and have a good look at your steering wheel, if it is noticeably off centre when stationary, then this may indicate an issue
Feeling vibration when driving through the steering wheel. The vibration may be caused by your wheels having been knocked out of alignment. Hitting potholes, especially at speed can instantly cause a change, and you'll notice it here. This may lead to some serious issues if left unchecked, not to mention damage to the wheel itself.
Uneven tyre wear
If your wheel alignment is out, it will gradually impact the ongoing wear on your tyres. In most cases, it will wear unevenly, and you'll be up for the cost of new tyres sooner than later. Keep an eye on all four to see if there is a significant change.
Impacts on steering can be caused by bad wheel alignment, as you may not have the responsive control you normally would have while driving - and may start to feel a little loose.