  Privacy preference signals allow users to express preferences over how their
personal data is processed. These signals become important in determining
privacy outcomes when they reference an enforceable legal basis, as is the case
with recent signals such as the Global Privacy Control and the Transparency &
Consent Framework. However, the coexistence of multiple privacy preference
signals creates ambiguity as users may transmit more than one signal. This
paper collects evidence about ambiguity flowing from the aforementioned two
signals and the historic Do Not Track signal. We provide the first empirical
evidence that ambiguous signals are sent by web users in the wild. We also show
that preferences stored in the browser are reliable predictors of privacy
preferences expressed in web dialogs. Finally, we provide the first evidence
that popular cookie dialogs are blocked by the majority of users who adopted
the Do Not Track and Global Privacy Control standards. These empirical results
inform forthcoming legal debates about how to interpret privacy preference
signals.
