Each planet has a sigil or seal that is designed to block that planet’s energy. Imagine the magick square as the accelerator and the planetary seal as the brakes. Blocking a planet’s energy can be useful in times of retrograde, or when your desired intent is to block the negative effects of a planet. Lets look at Mercury for this example. Many people are effected dramatically when mercury goes retrograde. One of the most common things most often adversely impacted Mercury retrograde is communication. If for example you had a meeting that was important to your career during a Mercury retrograde, you could block the mercury energy by placing the planetary seal over the magick square of Mercury, thus eliminating the effects of Mercury retrograde for you. Bear in mind that when you block a planet you are blocking ALL of the effects of a planet, so this could work against you. Although sometimes blocking a planet temporarily may be appropriate usually a sigil designed to filter the negative effect may be a better way to handle a situation.