First and foremost, let's understand the difference between swallows and sparrows. They are NOT the same thing. They are not the same bird and have vastly different meaning between them. The words swallow and sparrow cannot be used interchangeably. Swallows are a traditional old-school tattoo symbolizing enduring love that first appeared on sailors during the World Wars. Because swallows are known to always return home to San Juan Capistrano each year without fail, it was believed that sailors with a swallow tattoo would always return to their homes and families as well. Because swallows never fly too far from home, the sight of a swallow by a sailor was a symbol of hope; it meant they were close to land. Sailors with one swallow tattooed on them had traveled over 5,000 miles and a sailor with two tattoos had traveled over 10,000 nautical miles and denoted a very experienced sailor. If a sailor had the misfortune of dying at sea, legend had it that a swallow would carry his spirit to heaven. And if a sailor had a friend who passed away, he may get a tattoo of a swallow with a dagger through it's breast. But swallows are also an enduring symbol of love and loyalty, as swallows are monogamous creatures. They choose only one partner and will mate with them for life.
Many swallow tattoos were modeled after the barn swallow native to Europe. Blue in color, with a long, forked tail, barn swallows make their nests out of mud and are believed to represent the free blue sky and eternal happiness.
Source : http://hubpages.com/hub/Tattoo-Ideas-Sparrows-and-Swallows