alerts us to the news that, back in the day, skywriting was patented (see patent below) and that there were advertisements warning people not to infringe
. This particular ad was published in 1924 in Aviation Magazine.
If you can't read the warning, it states:
Warning: The process of forming Morse or written signals in the air by means of smoke or other visible trails emitted from an aircraft and the apparatus used in connection therewith are covered by Patents issued and pending in America and abroad. Vigorous action will be taken against infringers.
It seems some things just never change.