Generally speaking, if you must reveal a trade secret to a third party, you should have an intellectual property attorney prepare an underlying agreement which includes a statement as to what constitutes a trade secret and what the marking requirements are. A typical marking requirement may be simply "Proprietary material belonging to NAME". Often it makes sense to purchase a stamp with the appropriate phrase to facilitate the marking. For trade secrets that are intangible and cannot be directly marked, such as a process, consider the following steps:
(1) carefully define the trade secret in the underlying agreement
(2) mark the physical area where the process is carried out with a restricted access sign; and
(3) institute measures for restricting access to the trade secret, such as a sign in sheet and access verification check.