"You know what I mean. It's no use being unseen if people can find you in the first place!"

Strange takes Joker's laughter in stride, shrugging slightly. He knows he's right. Being invisible doesn't meant that one's completely hidden away, whether it's via hearing, magic or other methods that they could be spotted. If Joker learned invisibility, there would be ways to find him, even if it was something as simple as 'chuck a rock in his general direction.'

"I was able to piece Childermass's stealth spell back home, I'm certain I'll be able to piece out whatever you end up with."