What seal does Petyr Baelish (Littlefinger) use for his letters?

Question

Petyr Baelish a.k.a Littlefinger comes from House Baelish whose sigil is "a grey stone head with fiery eyes, on a light green field". We also see he has crafted a mockingbirg to use as a personal sigil.

Letters/correspondence in Westeros are sealed with 1) the house sigil in wax or 2) the emblem of the position (e.g. the Hand of the King).

So my question is, what does Littlefinger use to seal his letters? I see three options:

1. Sigil of House Baelish
2. Personal Sigil
3. Emblem of Master of Coin (if their is one)

Problems I have with each:

1. Littlefinger seems on distancing himself from his humble background and creating a new identity, which would lead me to believe he would use personal sigil (as we see on the ship's sails he uses to kidnap rescue Sansa).
2. Would other Lords recognize his personal sigil? I know Baelish is infamous as Master of Coin, but do all the Lords know his name directly? Would it matter, since once the letter is opened it is also signed?
3. I am not sure that the Master of Coin is shown to have its own emblem like the Hand of the King does. Also, he does not hold this position anymore.

Answer 1

According to the show, he uses his personal mockingbird sigil.

Here is a picture of the letter Olenna receives in S5E7:

And from the episode summary:

Returning to her palanquin, Olenna receives a letter bearing Petyr Baelish's seal.

Answer 2

Adding a couple of things to Justin's answer.

We know very little about the laws of heraldry in Westeros and how they are enforced, but we do know a couple of things:

1. You cannot use a sigil recognized to be someone else's. In The Hedge Knight, Dunk is told he has to change the sigil on his shield since he has no claim to the Pennytree name and sigil.

2. You can change the sigil you were born with and make that the sigil that reprsents you and your descendants. The Karstarks are an ancient cadet house of the Starks, and have their own sigil. More recently, you have the Green Apple Fossoways who broke off the Red Apple Fossoways (changing the color of the sigil but keeping the name).

So it's quite proper for Littlefinger to stop using the Titan sigil in favor of the Mockingbird.

Answer 3

I also found that after being made the Lord of Harrenhal, he created a new sigil for his new house.

This lends itself to Littlefinger using his Mockingbird as his only sigil and that it will be widely recognized.