Odd dummy subject markers

[RonButters at AOL.COM]

A graduate student writes (in a paper on the semiotics of ethnic restaurant
design):

"On the sign it features a checkerboard pattern implying a tablecloth,
whereas on the building it is simply a solid green line surrounded by yellow."

I'm used to Southern substitution of "it" for "there," as in the second
clause, but the "it" in the first clause seems weird to me. Is there some matter of
emphasis here that is different from simply saying, "The sign features a
checkerboard ... "? Or is the author just responding to the feeling that he cannot
have a sentence with a noun-phrase "subject" that is overtly marked by a
preposition?

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