The trick is deciding when you're absolutely head on, or not. Sometimes you look close but are not actually on a collision course .................. As usual though, in aviation, there isn't a one size fits all answer.
The design of an Aircraft's navigation (position) lights are with this in mind. You cannot simply look along the nose (avoiding parallax) because the heading is not the track made good: e.g. off setting for drift by +/- 15 degrees is not unusual. The RED-GREEN-WHITE arrangement of lights should be understood. However, other than strobes navigation lights will not be easy to see during daylight. The basic rule is: 'a constant bearing indicates a a collision course and therefore should be treated so.