first response

The consensus is that I should reply to the note that was left in my mailbox. In a very polite way -- handwritten, apparently, is the way to go. So my friend Alex is going to copy it out for me. However, since I have no French people to call on right now, I'm asking all of the dozens of my friends who speak better French than I do to help me craft/edit this letter, so that I can put it in Le Conseil Syndical's head's mailbox on Sunday night (30 hours to go!). Hopefully, I will get it reviewed by an actual French person, but here is my first attempt. (Non-French speakers are welcome to critique the English version, below.)

A l'attention du Conseil Syndical,

J'accuse réception de votre lettre du 18 Décembre. Je tiens à présenter toutes mes excuses pour avoir pu malencontreusement oublier dans le passé de verrouiller le local à vélos. En effet, je croyais avoir verrouillé le local quand je l'ai utilisé, mais, malheureusement, j'ai dû oublié. Veuillez accepter toutes mes excuses. Veuillez croire que dorénavant je serai attentif à le fermer systématiquement à chaque fois que je l'utiliserai.

Peut-être serait-ce d'autre part une bonne idée d'y installer une affiche qui rappellerait précisément de verrouiller le local, genre aide-mémoire? Si vous ne pouvez vous en charger, je serais très heureux de pouvoir me rendre utile.

Sincères salutations,

...

And I think this says:

To The Building Council,

I acknowledge receipt of your letter. I regret infinitely to have forgotten to lock the door to the bike room. I had thought I had locked it each time, but it seems that I forgot on those occasions. Please accept my apologies. I assure you that I will be very careful from now on and that I will lock the door to the bike room each time I use it.

A good idea would be to put up a sign that says to lock the door, to aid memory. Would you be able to make this sign? If you cannot, I will be happy to make such a sign. With all my compliments,

...