Boot-shaped and pick up on

People, i've seen this phrase and I was really trying to understand.

It was an oral invite, though. I didn't get a *boot-shaped* invitation like everybody else. Don't think I didn't *pick up on* that...

I think *boot-shaped* is something special isn't?
And *pick up on* is be sad isn't?

Thanks in advance.

'Boot Shaped; I have no idea but 'pick up on' means to notice/to be fully aware of the meaning.