Hiring of an investment bank would be one sign.  Such bankers will, in my cynical judgement, be sure to leak news of a buyout, as they are paid in % of deal size.  

But in general, there are leaks galore in biotech situations.  People can't keep good news to themselves and will yak.  The insiders will front run good news by buying up their own shares one way or another.

Surge in volumes traded, unexpected increses in price etc would be the last shoe to drop.

So far, there are zero smoke signals.  So the share price remains trapped below $1.33 which is where I assume equity financing is taking place.