While it is not "forbidden" to smile at strangers in Japan, the social etiquette regarding eye contact and facial expressions is quite different from Western norms. In many Western cultures, a quick smile to a passerby is seen as a friendly, polite gesture. In Japan, however, people tend to maintain a "public face" (tatemae) that is neutral and reserved. Smiling at someone you do not know can sometimes be interpreted as confusing, overly intimate, or even suspicious, as it may signal that you want something or that there is a private joke the other person isn't aware of. This is especially true in crowded urban environments like Tokyo, where personal space is at a premium and social "invisibility" is a common courtesy. However, as an international visitor, Japanese people are generally very understanding and will recognize a smile as a sign of goodwill or a "thank you" during a brief interaction, such as at a convenience store or when asking for directions. A polite, slight bow of the head is often a more effective and culturally resonant way to acknowledge a stranger than a broad, toothy grin.