Currently I’m working on a file and all of a sudden I see this small mark but I have no idea what it is or how I can get rid of it. Any suggestions?
Hi Paul,
That mark is because you have used the sample color tool.
Just select the tool again (I), and right below the file menu of Photoshop you will see a “Delete” button, click on it and the mark is gone. 
http://img689.imageshack.us/img689/6761/tooli.jpg
Thank you very much Aurove, I didn’t even know how it got there! Thank you!
You´re welcome Paul. 
Maybe you accidentally click on the dropper dropdown tool menu… it happens. 
