Come on Web trekker - you are better than that :-)
No one would seriously recommend a BN20 for someone that wants to do signage, the cutting width is far too small. The silver bullet is a brilliant machine though.
Dye123, You need to be aware of some things that you may not have considered. Ideally, if you want to do signage, particularly outdoor stuff, you really need a UV Printer. You can get UV Print n Cut but they are really expensive and I know that there are serious print head issues with certain Roland printers and the magenta ink.
My personal recommendation would be a Roland SP540, its wide enough for most applications and has a track history of being a very well built machine. I would not purchase a Mimaki which is based on opinions of those who have switched and wished they hadn't. I have never owned one so its a bit unfair for me to comment.
With regards to a separate cutter and printer. The speed issue only comes into play when you are printing and cutting serious amounts of media. I know loads of companies who specialise in signage and/or stickers and the still do not require two machines. The speed issue really is a non starter. You also need to consider that two machines is a much larger footprint. If you have the space - fine, but remember that space costs money.
Finally, I will say that a machine for garments, stickers and signage is a sort of jack of all trades and master of none deal. You can do far more with an OKI White system from TMT with regards to garments, but you can not do decent signage. You can do good signage and stickers on on a print n cut but the garment quality will suffer. Only slightly but they are not as good in my opinion.