Set Phasers to Shun (or The Fine Art of Not Caring)

It's not pleasant to be ignored.  It's not nice to go unacknowledged.  It's even less pleasant and less nice when the act of ignoring or the absence of acknowledgement serves as a means to avoid having to care.

Because by showing that you notice someone, by acknowledging their existence - their basic presence - leads to a connection.  And a connection leads to conversation.  And conversation leads to awkward questions like:  "How are you?", "How is your day going?", "How did you end up in this situation?" and "What are your chances of changing the situation?".

And so it is, or at least that is how it seems, that the good citizens treat my friend who sells the Big Issue locally.
It seems that they avoid recognition of her, so they can avoid acknowledging her, so they can avoid conversing with her, so they can avoid being concerned with her, so they can avoid caring about her.

Not everyone.  But the vast majority of them (us).
Ignorance is bliss, unless you're the one being ignored.  It must be soul destroying to have so many people looking past you, through you, around you, at their feet, at anything else but you... anything else at all, just to avoid connecting, conversing, caring.
An acknowledgment doesn't have to be an invite into something that'll bind you like a rope or commit you like a solemn oath.
It's basic. And it's easy.  And it doesn't cost a penny.
Just look.  Just say hello.  Just smile.  Just stop for a moment.  Just notice.