Do they come to people and hope that we can hear them? - yes. I've ran into several that once they knew I acknowledged them were like..oh! you can see/hear me! I think they hope that people can hear them and roam around until they find someone that can.
Do we send out some sort of psychic signal?-Kind of. You ever notice that people who are happy are infectious? That being around them even if you don't know them or talk to them makes you feel better? People, animals, spirits, etc are susceptible to vibes that each other put out. As for a whole batman sign in the sky I don't know if it'd extend that far..but it might. I'd imagine it's a smaller though.
How do they know where we are? 1. finding us by sheer luck 2. word of mouth 3. knowing us before we're given our physical body.
How do relatives know where we are? Imagine facebook for your family but in a spiritual sense. They know you before you have your body, they know who you're born to, they watch you as you grow, til when you leave the physical body and rejoin them. There are so many spirits that when people move or what not that someone notices and passes on the word.
How long have they been trying to make me aware of them? As for your spirits that are with you all or most of the time, I'd imagine they were always waiting and hoping you'd see them. To know that they were there and loved you and wanted your best. However, how long they have been trying to make themselves known proactively I'd not know. That's up to them. Many times we have so many spirits around us that you'd not believe it. Most just don't want to change our daily lives so they make their presence scarce.
Did they help you to unlock your brain center? When you wanted to start looking they are there to give a guiding hand. So it's possible.
Sorry if my response seems formal with categorizing your questions. I didn't want to miss any.
One of these days I'll surprise you all and will know the answer to something someone else asks! 
OTB