Cherries are one of the most common garnishes in cocktails, they used to say, "olives for the dry, and cherries for the sweet." Maraschino cherries used to be made with real maraschino liqueur and marasca cherries, today's so-called maraschino cherries however, was no longer made from marasca cherries, they were bleached, soaked in food colouring and sweetened with sugar syrup, plus other flavourings. They may look nice and adds some colour to your garnishes, but I wouldn't dip these into my drink nor eat them. We bartenders often call them "mara-shee-no" cherries instead of the true "mara-skee-no" cherries to tell them apart.
There are some good substitute to it. For example you can use fresh cherries, but they are expensive and they only stay fresh for a few days; an alternative to that would be turning fresh cherries into brandied or bourbon cherries. These can be done by soaking pitted fresh cherries in spirit of your choice, with sugar added, and perhaps spices; place everything in a sealed container and let them macerate for 2 weeks. Now the cherries won't go off as quick and they taste fantastic. Or you can make your own authentic maraschino cherries, but macerating cherries in maraschino liqueur; sure you might not be able to get the proper marasca cherries in your area, but at least you get a very close flavour to the original.
Brandied cherries and true Luxardo brand of maraschino cherries can be bought either online, or in certain grocery stores, but they can be quite pricey. So I personally prefer to make my own, you can to use fresh ingredients, and you get to decide how you want to flavour them.