The Descending Triangle is viewed as being more bearish than the regular Triangle patterns. When a Descending Triangle is formed, lower lows are being made (typically a bearish sign) and quite often, lower highs are being made (generally seen as bearish).
With the Descending Triangle formation, a possible sell signal occurs when the support line is penetrated to the downside. Traders usually view the sell signal as being stronger if prices have been in a confirmed downtrend prior to the Descending Triangle formation and downside breakout.