if i install a visual from appsource it has a logo and a key telling that invalid license.
Does this mean that i use some formating invalid according free license or this will alway show for everybody if free license is used?
The Red key is an indication that you are using a feature that is a part of the Pro version. As per design, these features are available for the free version as well but with certain limitations. Logo will be displayed if you are using a free version.