Signs discouraging the use of smartphones in places where people are most likely to start conversing with strangers.
Most people like to socialize and make new friends/acquaintances whenever there's a possibility for it. However, social anxiety is the most vital discouraging factor when it comes to starting a conversation with a stranger. If a person is not brave enough to initially start a conversation, to avoid feeling unease being silent around strangers people usually turn to their phones to look like they are "busy". This discourages others from trying to talk to them. The result is often everyone "talking" to their phones instead. Such signs would make people think twice before turning to their phones and therefore bring the following benefits:
Make people try to overcome their social anxiety instead of escaping it.
Encourage social interactions between unfamiliar people.
Contribute to lessening tech addiction.
All lit takes is to design witty signs and hang them in places where spontaneous social interactions are most likely to happen, e.g. places where people smoke, public transport stops and inside the public transport itself, near some public benches, in bars, etc. The locals/frequent visitors of certain places would know best which places are the attractors of social interactions and where is best to hang the signs.
One might go different ways about designing such signs, but I imagine a "no smartphone" sign with a text written under, reading something like "turn to a fellow human to talk to, instead of your phone:)" or " you get enough internet browsing at home, public places are best for social interactions;)". If you have ideas for the design of such signs/phrases under them, please write them below.