86 Ill. Adm. Code 130.725
Display
Section 130
Section 130.725 Display
The taxpayer must conspicuously
display his certificate or sub-certificate of registration in the place of
business to which it applies. Wherever possible, the taxpayer must display his
certificate or sub-certificate of registration in the place of business to
which it applies by affixing such certificate or sub-certificate to the glass
part of a window or door which faces or opens upon a public street or highway,
or in some similar position. If no window or door faces or opens upon a public
street or highway, the certificate or sub-certificate must be posted in some
conspicuous place which is as near as is practicable to the entrance of the
taxpayer's establishment, and such certificate or sub-certificate must be
exposed to public view.