I like to keep any unnecessary stuff away from the user, but at the same time like to give credit where due.
So I include a credits screen that can be viewed by the user IF THEY want to.
The credit screen is a rolling text type thingy like you get at the end of movies and such. Before the credits start rolling it shows several logos all displayed using the fade in behaviour. Currently in this order: 1) Our logo. 2) HTML5 logo. 3) Contruct2 logo. 4) Our game title. 5) Our web site address.
When they finish the text credits start rolling. The text also include reference to HTML5 and a 'This game was created using Construct2, the coolest game making software out there' and a plug for Ashley and Tom pointing Scirra.com.
To me this gives credit where due, a plug for those that made it possible, but at the same time it is non-invasive.
Tom, although I've made one of my own, do you happen to have a "Powered By Construct 2" logo?
Yeah it would be nice to have an official 'powered by' logo.