By Pete Najarian, co-founder of OptionMonsterNEW YORK -- The iShares High-Yield Corporate Bond Fund ( HYG) doesn't show up on our tracking systems often, but Monday it saw heavy option activity that signaled bullish sentiment toward the market. Traders focused primarily on a select few strikes, starting with the June 95 calls, according to OptionMonster's tracking systems. They then shifted to the January 94 calls, which were sold, while the February 95 calls were bought as a bullish position was adjusted. Calls lock in the price where investors can buy shares in the fund, so if it goes up those contracts will generate some nice leverage. But these options will also expire worthless if the stock fails to move by their expiration dates. The exchange-traded fund fell 0.14% to $94.39 Monday but is trading at its highest levels since the 2008 crash. The junk bonds held in the ETF tend to follow the S&P 500, so these call buyers were actually looking for the stock market to keep climbing. Almost 18,000 total options changed hands in the fund Monday, more than triple its daily average in the last month. Calls outnumbered puts by 16,700 to 1,200, a reflection of the session's bullish sentiment. Najarian has no positions in HYG.