>Any body know what the following signs "@" mean?

It is just an example of what a phone may be. 

The speech rec engine does not care what character you might use to represent a phone, but since it is so time consuming to create your own pronunciation dictionary, you use the phoneset from some prexisting pronunciation dictionary. 

It's been a while, but I am assuming that @ was a phone in a non-VoxForge pronunciation dictionary that might correspond to something like AE in the current Voxforge pronunciation dict.