Topics/threads denoted by a blue thumbtack are called featured topics or sticky threads. These topics/threads are selected by Yahoo! because they usually offer content that is on topic, provide important information about a specific feature, contain guidelines for a board, or are simply something that many readers might find beneficial.
The best way to have your topic/thread selected to be featured/sticky is to follow our tips on writing a good message. It is not possible to submit a topic/thread for review to be chosen as sticky.