When strangers say "Hello" to you, it is generally considered polite and friendly to respond with a "Hello" or a similar greeting. Acknowledging someone's greeting is a simple way to show respect and create a positive social interaction.
If you are in a situation where strangers are likely to greet each other, such as when passing by someone on the street or entering a shared space like an elevator, responding with a friendly "Hello" or a smile is a kind and appropriate way to engage in brief social interactions.
However, it's essential to be mindful of cultural differences and individual preferences. Some cultures might have different greetings or customs for such situations. Additionally, some people might prefer to keep to themselves in public spaces, and that's okay too. Always be respectful and considerate of others' boundaries and comfort levels when engaging in social interactions with strangers.