A patent holder may only collect damages for infringing activity occurring after the infringer was given notice of the patent. The notice provided may be actual notice (such as a cease and desist letter sent from the patent holder directly to the infringer), or it may be constructive notice (providing a marking on your patented products, such as "U.S. Pat. No. 9,342,523").
More specifically, the patent marking statute (35 U.S.C. §287(a) states:
"In the event of failure to so mark, no damages shall be recovered by the patentee in any action for infringement, except on proof that the infringer was notified of the infringement and continued to infringe thereafter, in which event damages may be recovered only for infringement occurring after such notice. Filing of an action for infringement shall constitute such notice."
Thus, by failing to mark your patented invention, you may wind up only being able to recover damages for those infringing activities that occurred after notice was given.
More specifically, the patent marking statute (35 U.S.C. §287(a) states:
"In the event of failure to so mark, no damages shall be recovered by the patentee in any action for infringement, except on proof that the infringer was notified of the infringement and continued to infringe thereafter, in which event damages may be recovered only for infringement occurring after such notice. Filing of an action for infringement shall constitute such notice."
Thus, by failing to mark your patented invention, you may wind up only being able to recover damages for those infringing activities that occurred after notice was given.