If you're a shareholder in Barnes & Noble (NYSE:BKS), there are at least four reasons you might want to reconsider whether the investment is worth the risk.

No. 1 is the simple fact that its chairman and former CEO, Leonard Riggio, has apparently concluded that it's not. Two weeks ago, the ailing bookseller announced that Riggio had offloaded 3.7 million shares of his personal stake. And he did so, mind you, after a similar episode in December in which Riggio sold 2 million shares and claimed to not have "any intentions of selling more."

But while this alone is ominous, it's far from the only disturbing signal emanating from Barnes & Noble. Among others, the bookseller has experienced five consecutive quarters of declining same-store sales, and the CEO of its retail division said in January that the company plans to close one-third of its stores in coming years.

It's for these reasons that Motley Fool contributor John Maxfield notes in the video below that Barnes & Noble's stock "has only one direction to go: down."