The domestic cat and the bobcat look completely different, so it would be fairly easy to distinguish them. The bobbed tail cannot be relied on by itself, as there is a domestic breed of cat called the Manx that has a naturally bobbed tail, as well. However, this breed is a bit rare compared to all of the other breeds of domestic cat, which have a naturally long tail, so it does make for a good first rubric.
Other than a bobbed tail, Manx cats look identical to their domestic brethren :
Bobcats, on the other hand, look more like their cousin, the lynx :
There's also the component of size. Bobcats start life larger than domestic cats, and grow to a larger size in adulthood, with bobcat kittens weighing approximately 125 grams when measured at a few days old . Contrast that to the weight of domestic kittens at around the same age being about 100 grams .
Regarding Maine Coon kittens, yes, they have similar ears to bobcats, but it would again be difficult to confuse them, because of the other facial features (they lack the "mutton chops" that bobcats and lynx have) and the elongated tail :
- Breeding Habits of Bobcats in Utah, Jay S. Gashwiler, W. Leslie Robinette, Owen W. Morris, Journal of Mammalogy, Volume 42, Issue 1, 20 February 1961, Pages 76–84
- Moik, K., & Kienzle, E. (2011). Birth weight and postnatal growth of pure-bred kittens. British Journal of Nutrition, 106(S1), S32-S34. doi:10.1017/S0007114511003333