I have heard many times from many people saying 'it is love' or 'French is love' or 'Baltimore is love'. What does it exactly mean? Shouldn't they use lovely instead.?
This is a metaphor. A more concrete metaphor would be:
George is a big teddy bear.
George is not literally a big teddy bear; he exhibits the qualities of a big teddy bear. In the same way:
Baltimore is love
means Baltimore exhibits the qualities of love.
(Having lived in Baltimore, I can't say I agree with this metaphor, except in that it exhibits insane jealous rages, tunnel vision, and a damn-the-consequences attitude).