You can tell if you ask them, or better yet if you??re interested in them let them know it. You??re a sagg so I suspect that you are known to be blunt so this shouldn't be a problem for you. Besides, a Libra loves to be flattered and when it's given to them in a sincere manner by someone they like, they have no problem returning the favor. Libra??s are huge flirts. However, if they are unsure if the feeling is mutual they will almost never come out and say it. They would much rather just flirt with you, and charm your pants off until you melt.
Once you know for sure they like you, they will enjoy a bit of cat and mouse. They like a chase (the males) anyway. However you cannot make them feel as though they are chasing you for their health, they have to know you like them too first. So long as you don't make them feel as though they are wasting their time, game on. To spice it up try to dress to impress, always smell mouthwatering or just really really good (this is a plus), and don't be afraid to go that extra mile in the morning or whenever you know you??re going to run into them, chances are they are doing the same if they are going to see you and they will appreciate seeing it. A libra??s love is worth it. So long as it's pure.
CAUTION: If this is a Libra guy, I strongly suggest letting him for you first. Go read —Understand the Libra Male?? by Alibra. The gal knows her stuff. I should know. Since I am her! Lol. Can't figure out my darn password for that account. Oh well..