Non Buddhist can say Hello to Buddha or Monk?

I understand this hand sign is to respect and say hello to Buddha or greeting to monks. **Ques 1:** Where is this written in Sutta exactly what the hand sign means? **Ques 2:** Can non Buddhist bow to Buddha when they visit temple? Most articles says no. If no, then what other hand sign more standard or more acceptable widely to greet Buddha or Monk from Buddhism perspective? Post note: Buddha is not for Worship