I have just figured out there are two Ectors, took a while for a beginner like me to figure that out. :)

The younger Ector de Maris has a shield that can be found, but I can find nothing about Arthurs foster father.

Are there any records about how old Sir Ectors shield would look? I assume it would be blue, like Kay's.

W

Heraldry is still takings its baby steps when Arthur becomes king, so the rules are more fast and loose. I think Sir Kay's keys represent his own achievements as a Senechal rather than anything his father did, although keeping the familial motif of a blue field would be a nice touch. I am unaware of any heraldry assigned to Sir Ector in the literature, but I am no Arthurian scholar.