There is a principle of al tiftach peh l'satan (Ketubot 8b, Berakhot 19a). I would like to know if this concept is specifically limited to speech. Would writing, signing, or some other form of (non-verbal) communication fall under the parameters of al tiftach peh l'satan?
This is the equivalent of the English phrase Don't tempt fate> As a result it could involve any means that would allow the Satan to call for a judgement against you from the heavenly court. This could involve any phrase or sign or action. Since most communication by people is verbal, that is the usual reference.
An example of this is that people leave the shul for Yizkor if both parents are alive. This is not that they do not want to be present during the memorializing of the dead, but that it looks as though they are deliberately refraining from tefilah. This action is like al tiftach peh lasatan.
I have seen references to do not smoke as involving al tiftach peh lasatan because one is endangering ones health. In that case as well we see that it is an action rather than just speech.
It also teaches that one should not even give slight recognition to his instincts, "as once the dam cracks, its bursts". The instinctual drives are like a surge pushing forward all of the time, a brief outlet can cause a tremendous flow of energy into the instinctual. Therefore, not even "opening one's mouth" is the best gaurd against the instincts.
Literally: Don’t open your mouth (gateway) to the devil Idiomatically: Don’t tempt fate
This unusual phrase is actually still in use today. It is brought down by the Talmud (Ketuvot 8b, Brachot 19a) and refers to the idea of not inviting misfortune. In Brachot, it is part of a discussion on the obligation to say the Shema Yisrael prayer (which is time related), during a funeral, and the idea of mentioning how we ourselves have sinned and not been punished. Abaye said “Don’t even say it since we learned from Rav Jose ‘Leolam al yiftach adam piv lasatan’ - Never open your mouth for the devil – which could invite punishment. This phrase, by the way, is totally universal and can be found in dozens of languages and cultures from Thai to Swedish to Irish. Similar to the Hebrew idea of tempting fate, we find it in medieval English as "Speak of the devil and he doth appear." The idea behind this seems to be the superstition that by mentioning the devil by name you can cause harm. Today, in most cultures, the phrase is far more lighthearted, referring to a person who shows up when you mention him. In Hebrew that phase would be “Medabrim al ha-chamor, (ve-hinei hu ba)" - Talking about the donkey, (and here he comes).