The maintenance of a Sell rating suggests that Citigroup analysts believe Vornado Realty's stock may still underperform the market or its sector. However, the increase in the price target from $12 to $18 could imply that the downside risk is not as severe as previously thought, which may slightly mitigate negative sentiment among investors. The impact is likely to be negative in the short term as the Sell rating predominates, but the raised target provides a less bearish outlook than before.