That's what chunks are for.
Create a chunk with that text and place it in all of your templates.
Its great but normal user will change the value of chunk, as i dev i know and i can but how simple user can change text if he want.
I want to give access to client that he changes text whenever he wants.
discuss.answer
The ClientConfig - Extra could be an option
http://modx.com/extras/package/clientconfig
Thanks Bruno, it really helped me.!!!