Errors location are marked with an error marker.
Successfully compiled are marked with an @ icon .(may differ from this picture)
Ignored annotation (f.e. regular JavaDoc) are not marked at all.
Simply remove the backport175 nature from your project.
If you are using an annotation.properties file, you need to register it in your module build settings. Right-click on your module, select Properties, and configure the Backport175 annotation.properties entry here.