Perhaps you get touched of the sight of old people staying on a bench at the park, throwing food at the nearby flock of pigeons. Pigeons are funny to observe from the side, however, we only see the bright side. In reality, pigeon droppings could spread diseases and damage your property. There is a variety of measure you could take to prevent this from happening. Pigeons are used to living in urban areas and move around people. They feel no initial fear when people invade their space, which makes them a tricky bird to deal with.
Furthermore, they have no actual natural enemies, which allow them to freely breed and grow their population rather quickly. A popular trait which was "exploited" by humans was their ability to find home. Pigeons were used to carry letters through large distances.
This ability enabled the bird to populate the whole planet. On top of that, pigeons could potentially carry the threat of spreading a disease, which is why they shouldn't be allowed in areas with children. Another issue is their nature to damage surrounding both directly and indirectly. Their feces attract other wildlife nuisances as rats, flies, and mice, which feed on them. Even if that doesn't happen the feces themselves could cause corrosion or massive acidic stains, which destroys the life of roofs, in some cases even halves it.
We are sure you've experienced the "lovely" imaginary of pigeon feces on your car paint, which should be dealt with before permanently damaging the color.
One of the most effective methods is to buy anti-roosting spikes. The latter are placed on the locations where the pigeons go to sleep, that discourages them to land and creates a pigeon-free environment. Such spikes could be observed on the roof tops of many municipal buildings in the big cities. They are cost efficient but might require some time to set up. Either way, they are certainly worth the time and money spent.
Another way to prevent them from coming on your roof top is by using a gel-repellent. That's a temporary solution and works well for people that live under rent. It makes the surface sticky, and the birds are unable to perch, which will force them to move to another location. However, time and weather takes its toll on the substance, and that's why you have to reapply it once every few weeks.
If you live in a house in the suburbs, you should make sure that all of your trash bins are closed and that you don't leave any food out in the open. Inspect your property for places that might be appropriate for pigeons. Those might be vents, soffits and large gaps where they could nest up. If you allow them to set a nest, the problem will become twice as annoying due to their strong memory. Even if you destroy their nests, they will keep coming back.
Other methods include ultrasonic devices, which send out a sound causing the birds to flee. The only disadvantage with this option is its price and its unavailability. Its relatively new on the market, therefore you'd have to search for it for a bit.