Destroying sigils is often touted as a non-negotiable step with burning being the go-to suggestion but I find this mindset to be a bit restrictive. In reality, destroying a sigil by burning or other means can be useful but it really depends on your preferences and what methods you work with. For example, if you’ve made a clay amulet with your sigil on it, burning it won’t work very well and might even be counterproductive to your goals.
I separate sigils into two camps: fast action sigils and long action sigils. Fast action sigils are those you come up with and activate on the fly. These are the scribbled sigils written on the backs of receipts or in notebooks, drawn on arms in a hurry, or otherwise created and cast in a short amount of time. Destroying these is optional. Some people find that destroying them after helps to both seal the activation and keep them out of conscious memory while others don’t see much effect from it. This is an area where experimentation is encouraged to find what works best for you. Remember, magic is about getting results, not about “doing it right”. If it works and gets you better results that that is the right way for you to be working magic!
Long-acting sigils are those that are designed to stick around for a while. They might be etched into jewelry or amulets, incorporated in a jar spell, used in a piece of art, written on a little scroll and used as part of a larger spell. These sigils are more premeditated and typically are designed to work over a long period of time. Because of this, destroying them is often not a good idea! At least while your spell is still working, it’s best to leave these sigils be. Once the spell is complete and you have the desired results, you can dispose of the sigil in the same way you would dispose of other spell remnants.