Oh wow. You can’t even trust your printer now ‘cos it could expose potentially incriminating information about how you are using it.
The problem is that most new printers print nearly invisibly yellow dots that track down exactly when and where documents, any document, is printed. Because the NSA logs all printing jobs on its printers, it can use this to match up precisely who printed the document.
Source: Errata Security: How The Intercept Outed Reality Winner