How can I tell a bike is safe after a crash?
The easy way would be to get a qualified bike mechanic to take a look at your bike for less noticeable problems. 


It's not safe to ride a bike if the frame has been noticeably disfigured.
Re-adjust the wheel to be aligned to the handlebars. The wheel tends to twist after crashes.
Go through the final safety inspection you would normally go through, check the tyres, brakes. Replace the brake cables if they are frayed.