Tumblr has been undergoing a rapid growth spurt lately, rolling out new features and seeing a marked increase in international traffic. One thing the company hasn't mastered, however, is how to turn a profit — but a new "highlighted posts" feature may provide a clue on how it's planning to get there. The feature itself is pretty straightforward: for one dollar, you can mark a post as highlighted, and it then shows up in your readers' dashboards with a customized sticker and alert to the side ("new," "breaking news," and "PARTY!!!" are amongst the more than 40 available options).

Tumblr has famously rejected including ads as part of its service, with founder David Karp saying last year that the company was looking at expanding its template theme marketplace as a way to generate additional revenue. If highlighted posts are any indication, an expanded marketplace may not be enough, and we wouldn't be surprised to see Tumblr try out additional pay services over the course of the year.