CE - Key of...what?

Welcome to Clockwork Cafe

This is a place, where you can rest after a long day, have a nice cup of Tea, or just order a Coffe, and sit back in one of our comfortable chairs.
The name, "Clockwork", represents perfectly the atmosphere: cogs, pocketwatches and steam-machines everywhere. Between these surroundings peoples can enjoy every minute and every drop of their ordered drink.
Come by anytime!
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One bonus point is given for the one, who notices first, what is the meaning of the symbolism on the picture, related to the key. Its an easy one, i am sure you can find it out! ;]
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Contest entry for 's Key of Truth contest.
Her character, Mildred, belongs to her. I only created the picture itself. I hope you will like it! ^^