Call sellers looking for a top in Sina

As Sina goes parabolic, some investors are taking the other side of the trade.

optionMONSTER's tracking systems detected a flurry of call selling in the Chinese Internet stock, which has more than doubled in the last six months.

Most of the activity focused on the December contracts. Investors wrote calls at the 75 strike for about $1.05 early in the session, then as much as $2.50 in the afternoon. The December 80s were sold for $0.25 to $0.56. Volume totaled 2,574 and 1,356 respectively.

There was similar activity in the December 72.50s calls, according to optionMONSTER data.

When investors write calls, they agree to sell a stock at the agreed strike price. Shareholders often use the strategy to lock in an exit price, so heavy call selling usually reflects a belief that a stock is near its top.

SINA rallied another 5.76 percent yesterday, ending the session at a new all-time closing high of $75.62. It's been surging as investors price in the growing popularity of its Weibo blogging service. There was also substantial short interest earlier in the year, which apparently helped drive the gains. Pete started pounding the table on the name back in September.

The call selling pushed total option volume in SINA to 10 times greater than average in the session.

(Chart courtesy of tradeMONSTER)