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Post when and where relevant, and include "when in Rome, do as the Romans do." If signatures are commonly used and welcomed, feel free to include one.
Aim for (earned) mindshare, respected brand awareness, etc... not PageRank.
Remember... even if you CAN get a little bit of extra PageRank, it sure isn't worth annoying entire swaths of folks via inappropriate or otherwise obnoxious link drops.
Think long term respect :)