Observe the appearance and bearing of your chief executive. Most get depressed at the thought of laying off staff. Long budget discussions are a bad sign. If your company works on a calendar year, the budget is probably discussed in September and finalised in October. A senior person in your department leaves in unexpected circumstances.
Destabilisation is often the precursor to redundancies.
Making people unhappy is seen as a cheap way of getting rid of them in some organisations. Rival companies start laying off staff. Senior management begin talking about competitive pressures and the need to improve productivity. You don't have enough work to do or the amount of work for your department is cut back. New people are brought in to manage your company or it is taken over.