1. verb To share particular information online in order to raise awareness of it or expose it to a larger audience. Hey, will you signal boost our charity event this weekend? If you retweet those trolls, you're just signal boosting them, and that's exactly what they want.
2. noun An increase in the awareness or exposure of particular information online, typically achieved through the sharing of it by someone with a large following. Hey, if you could share our charity event, you could really give it a signal boost. Don't retweet those trolls—you're just going to give them the signal boost they're looking for.