If I am the only person who has to cover their tattoos at my job, is this discrimination?

Contrary to popular belief, almost all "discrimination"--or unequal or differential treatment of employees--is legal. Only those forms specifically prohibited by law, such as discrimination on the basis of race, religion, age, sex or 40, or disability, are illegal. Other than that, an employer could require one employer to cover his/her tatoos and not another if it chose.

And even if you believe that you are being singled out due to your membership in a specifically protected category, like those above, if the employer can nonetheless show some non-discriminatory rationale or reason for what it is doing, it will most likely be legal. So, for example, if you have many more tatoos; or they are are more "lurid" or colorful or larger; or their subject matter is less appropriate; or you have them in different locations; etc.--in any case like this, if your tatoos are different than other workers' tatoos, the employer can ask you to cover them but not require others to do so, too, even if you are, for example, the only member of a minority, the only employee over 40, etc.