Certainly purity seals are the bling of the Inquisition, Grey Knights and Sisters of Battle. The question is can they get enough of them. The GW provides molded on purity seals on some minis and customizable purity seals for some such as Grey Knights. But if you want to up the purity and worship of the Dead Emperor stakes more purity seals are needed. There are a number of options to getting more purity seals to add to minis. ForgeWorld sell a packet of resin purity seals for £6.50 plus p&p. These seals are well sculpted as might be expected but are a bit pricey for what you get.
The pictures speak for themselves I think. Stick the bits of paper together
Undercoat and then paint.