Many brands of English are non-rhotic. In UK orthography, in a Vr combination, the r is not pronounced and the V may be changed, too: hence, erm is pronounced with a non-rhotic schwa, and approximates the US transcription um. I was looking into this the other day, as somebody pointed out a bit of strangeness in the opening chapter of Winnie the Pooh, with a cryptic reference to Winnie ther Pooh. I told them it was probably the difference between thee and thuh which alternates in pronunciation and meaning. See this interesting take on it.

Ceci n'est pas un seing.