For an IPO, expect to see the company redoing the entire finance system - public companies have very strict reporting requirements that startups don't implement. Also, if they start withholding more information, there's a lot of things that you can't announce as a public company(or becoming one). Of course, that could be the opposite and the numbers are so bad they wont talk about them. One last thing is auditors could indicate either - due diligence in an acquisition, or prepping for an IPO.

In terms of raw numbers, there's not as clear a thing - I've been in companies that were acquired for doing really well, and others that might not have been able to pay payroll in a month.