The Bitshares blockchain supports many coins and the ability for anyone to create their own coins (for a fee). Sometimes new tokens do their ICOs on the Bitshares blockchain and they airdrop their tokens to users. Other times people create tokens that have no worth, airdrop them to people and then create fake market activity by trading it with themselves hoping to lure people to buy them.
In both cases, its not a problem to just ignore the coins in your wallet. If you are getting too many, you can just click the “Hide” button in your dashboard that will hide the coins. You can always view them on the hidden tab or “Unhide” them. Or you can sell them.
However please be aware that some scammers can create coins (e.g. RIPLE) that seem to be something they are not. In this case, the RIPLE token is not the RIPPLE cryptocurrency.
It is best to do your research!