As is often the case for Pathfinder there's an archetype for that:
This archetype allows you to disguise your divine spellcasting as non-divine, even as alchemical tinctures or arcane magic. In addition, it allows you to substitute a far less obvious sign of your faith than a typical holy symbol.
When the hidden priest uses this ability, he must still provide any divine focus components for the spells he casts. However, the divine focus doesn’t need to be an obvious symbol of his faith. It could be a small coin, tattoo, or garment bearing the symbol, whether presented openly, disguised, or hidden within a larger picture. For example, a hidden priest of Sarenrae may use a coin with an ankh or sunburst, a complex tattoo or scar that has an ankh shape hidden within it, a glove with an ankh stitched on the inside of the palm, and so on. He must use this replacement divine focus just as he would his true one (for example, he couldn’t leave the coin in his shoe).