I was asked recently how one makes repeat use of a sigil, if one actively tries to not remember what it does. The first thought that came to mind for me is that it doesn't matter. If something is important enough for me to ensigilize it, and not discard the sigil after using it, then it is important enough to use again if I feel like it, whether or not I know what it does.
While that was a fun, flippant answer it did not really address the question. What was being asked was how one might re-use a specific sigil to re-accomplish the same task. I think the topic in mind was relaxation, or something like it.
That is a trickier question because I don't think most sigils are intended for repeat usage. A lot of sigils are one-shot spells, so you don't generally worry about long-term repeat use. Even those that might have long-term applications may never see a second use. Sigil magic is very simple, from concept through application, so there is a strong tendancy to make a new sigil each time, even if the objective is similar to that of a previous sigil. I think there are a number of reasons for this:
Many spells that might have useful repeated applications can have their effects accomplished without the use of a sigil. For example, in response to the question about a repeat-use sigil for relaxation, I recommended self-hypnosis. The person seeking relaxation could, say, find a small, polished stone and use a post-hypnotic suggestion like this: "whenever I hold this stone in my hand, I will allow all tension to flow from my body, easing each and every muscle to a relaxed, comfortable state." This would produce the same effect, without having to concern the operator with the fire-and-forget philosophy.
For sigils that bear repeat usage, such as one for lucid dreaming (and for purposes of this discussion, let us assume that self-hypnosis, trance meditation and other methods are either unavailable or undesirable for one reason or another), there are still ways to use them.
The easiest is to keep it around one all the time, someplace one will see it on a daily basis. This works because the benefit will be there, but one need not worry about what it is. Doing something like that with a sigil for lucid dreaming will promote lucidity in one's dreams over time. It may not leap into effect the first night, but over time its impact will be felt. It helps if one periodically jump-starts it with a touch of gnosis, but its presence in the background, especially if one doesn't make a big deal about it, will help it ease into one's deep mind on its own.
Another way is to have some sure-fire means of distracting oneself. For example, if one can get quickly and completely lost in a novel, then it may not matter if one knows what the sigil is. One might simply fire off the sigil, put it away and throw oneself into a book, forgetting all about the sigil and its purpose.
While the second way can be quite effective, I prefer the first for long-term use. It simply takes less effort over time. I don't want to charge the same sigil on a regular basis, much less have to spend time distracting myself from it afterwards. I prefer to post those sigils on the walls of my room, or similar, where they can get their work done without distracting me.
Four Winds Bar