BNO, or "be on (the) lookout," is a helpful abbreviation often used by law enforcement officials or security personnel. However, there are several other synonyms that can be used instead of BNO in different contexts. One alternative could be "watch out for," which indicates a need to be cautious and aware of potential dangers. Another synonym could be "keep an eye on," which is commonly used to refer to monitoring a situation or individual closely. Additionally, "be vigilant" or "remain alert" can be used to convey the same message as BNO, inspiring the need to pay attention and remain sharp at all times.