Welcome to the site!
To help with translation since most here are from the US, please post in English. You can use an online translator such as this one from Google.
To answer your question about the Roush script on the instrument dials, I've had a Roush Mustang in my possession for a short time and it did indeed have the inscription in the cluster. Here is a picture of the dash inscription from the one that I had:
I don't know what all Roush does with their cars, but this 07 has other stuff that's been branded, like the gauges.
Of course this is from a different model year and body style, maybe someone will be along and give you better tips than I can, but I'd think that there would be more evidence than the sidepipes.
One other thing that I think I notice from that pic is that the rear bumper doesn't have the Roush ground effects like I see in different Google pics, like this one for example.
If I had to guess, the seller (or a previous owner....) installed the side pipes on a run of the mill GT and called it a day.
I don't remember if there was one on the passenger side, hopefully someone else will chime in and give you an answer.
