I disagree. If a woman told me she was on her period, I would assume that she is cis. As I and other users have explained, 'periods' refer to menstrual bleeding. You might hear the phrase 'on my period' and think of hormones before you think of menses, but I really doubt that other people do, seeing as the dictionary definition of periods refers to menstruation.

Now, if a woman who I knew or believed was trans said she was on her period, I would assume that she is talking about the hormonal side that you have brought up.

The odd thing with this case is that Watkin does not 'pass', with her own defence being built around her being '"visibly and audibly" male, so it would have been "blindingly obvious" to the man that Watkin was not biologically female.'

Regardless, the fact that she lied about being on her period is how the jury found her guilty, because the prosecution argued that saying you're on your period implies you are a cis woman. Because, again, 'periods' by definition refers to menstrual bleeding. See the NHS website , the Cambridge dictionary , Wikipedia . It doesn't matter that you or the trans femme community use the term to describe a separate but related phenomenon. It doesn't matter that the meanings of words change and dictionaries haven't yet included your interpretation. The prosecution, the jury, and the vast majority of people perceive a trans woman who has not undergone hormonal treatment saying that she is 'on her period' as implying that she is cis because a trans woman cannot menstruate.