Lets figure out what all can be effected if the car gets a nasty hit from underneath:-
Chasis -- highly unlikely, the first indicator will be mis-alignment
Gear box and oil sump -- oil spill or leakage are thhe indicators
Exhaust sys -- engine sound changes
Speed-o-meter cable, self explainatory
Cng line -- you wouldn't be here making a thread
Shocks -- extra thumps and jumps are the indicators (driver knows the difference)
Other items of suspension -- play in steering or mis-alignment can be the indication
Make your own assessment and drive safely, cheers