What are some signs to look out for if you suspect your company...?

Question

is either going to do a mass layoff or is being bought out by another company?

Answer 1

Rumors. Your manager and other managers get together for meetings. Stricter rules come up.

More supervision.

Answer 2

Before companies are acquired, the acquiring corporation usually will do an extended period of "due diligence" where they will review the target companies books and records.  If your company is for sale, chances are several firms will visit the main office to perform their due diligence.  If your company has had many visitors (professionally dressed) and these visitors have stayed long hours in conference rooms with senior managers, they could be reviewing your company.

Layoffs are more difficult to predict.  If your company is not doing well, they could resort to layoffs.  If it is a public company, read their latest quarterly earnings reports and see what they say about labor costs.  See what your competitors are paying for similar jobs.  If your managers change the normal course of job evaluations, they may be trying to determine which employees to keep.