Hi Frank. I'm not aware of an API or library devoted to time series pattern recognition. Have you tried googling "C# time series analysis"? There has been a lot of ink written on patterns so I wouldn't be surprised if someone has tried to pull something together. It would be interesting to try to figure out how to fit an existing .NET library into RE's structure. On the other hand if you are interested in just a few specific instances I'm sure they can be coded within the RE ecosystem. ("Time Series" opens up a vast arena, not the least of which are packages in the "R" programming language that can be interfaced to .NET for example. One can get to overkill in a hurry...)
(Welcome too to the Yahoo group. It is an unofficial venue for topics that might be tangential or incidental to the specifics of RE technology. Anything to do with the technology of automatic trading, as it might relate to RE, is fair game on the group. Perhaps it helps keep clutter off this forum? [grin])
(A basic library is http://ta-lib.org/. There is a .NET version. It includes some candlestick pattern matching. I am not aware of its use within RE.)
See also Yahoo group about applying RE.