Large file named 'etc/nginx/on' for nginx on Ubuntu

As far as i know, but i may be wrong, no such directive exists : access_log on;

I suspect that this directive makes NGinx write access log in file on instead of the file you specified using access_log /var/log/nginx/access.log;

Access Log can be disabled using access_log off;, which is an existing directive.

To keep Access Logs remove access_log on;, then it will write logs into the file specified in your access_log directive : access_log /var/log/nginx/access.log;

To answer : yes it is safe to delete this file (or backup it -move it elsewhere- if you want to keep track of these access log).