A ratio near or below 1 is ordinary. A ratio of 5, 10 or 30 means the day's trading dwarfs everything already outstanding, which usually signals a deliberate new position rather than routine two-way flow.
It is a screen, not a signal. High ratios appear constantly in illiquid far-dated lines where open interest is tiny to begin with, and the trade you are excited about may be one leg of a hedge whose other legs you cannot see.
Example: the XYZ $55 call has 400 open interest and trades 12,000 contracts, a ratio of 30. Worth a look. The XYZ $80 call has 3 open interest and trades 60 contracts, a ratio of 20 — statistically identical, practically meaningless.
Related: option-volume, open-interest, unusual-options-activity, options-flow