Typically used proceeding a # when updating your social media status, nerdswag denotes that you believe you're activities are typical of the stereotypical nerd. A "#nerdswag" in a post necessarily implies that you don't care what people think of your nerdy activity or achievement.
An easier way to think of it, is simply looking at the word. Nerd + swag = nerdswag. All the intellectual strengths of being nerd, and all the social benefits of having swag.
"I'm worried that this 1,000 word paper is gonna turn into a 2,500 word paper; and the professor only asked for 5 resources but I have 17. #nerdswag"
"I'm seriously considering taking 17 credits next semester. #nerdswag"