Sina.com (SINA, news, chart, volatility) is seeing relative weakness and options activity is running two times the usual Monday. Shares of the Shanghai, China Internet company are down to $26.00. There is no news to explain the $4.90 per share price drop or the uptick in volume in the December 25 puts. 3,480 contracts have traded, compared to open interest of 3,107. Two thirds of today’s volume is trading on the offer. Some investors appear to be buying these puts on concerns about further downside in the stock price. Implied volatility has lifted to 90, from about 70 late Friday.