Current ASF icon always was kind of placeholder, and I think it would be a good idea to eventually update it for something more decent.
I'm not an artist, and my graphical skills are awful, so I'm opening this issue to allow people to contribute, as well as vote (through GitHub +1s) on icons so we can choose the winner, in case there will be more than one.
General guidelines for making ASF icon:
In general, 184x184 ASF application icon, preferably with ASF text inside (but not mandatory), the design is up to you.
Your contribution will be included on ASF Apache 2.0 License. You will retain rights as an author, and allow ASF to use the icon freely in various places (mainly for ASF program icon as well as Steam Group avatar).
Each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form.
I don't want to give any fixed timeframe, but let's say that I'll start looking at contributions in a week from now. I don't know how many contributions there will be (and if any at all), so the final decision is still based on my sole discretion, but I'll definitely take in account GitHub +1s as well as general feedback.
Contributions can be attached either in this issue on GitHub directly, or on my e-mail: JustArchi[at]JustArchi[dot]net. Please include your image as attachment, and preferably leave a nickname so we know who is the author, unless you'd like to post anonymously, I don't have anything against. Contributions sent on my e-mail will be re-posted on GitHub so everybody can see them and vote.
I don't have any kind of special reward, as ASF is non-profit project, but I'll definitely leave proper credits as well as gratitude of not only me, but thousands of users. Thank you in advance for all contributions.

PSD & ICO:
ASF Icon.zip
Thanks for having such a great project enlighten our Steam community!
(I would like the option to keep the current one.)
@Luckz
Icon can't be easily configurable, it's always built-in, and I must eventually decide which one I want to stick with. I also like current one, but it's not only placeholder that exists since V0.1, it's also an icon I don't have full rights to use.
I'm always open for suggestions and solutions that satisfy majority of people, but icon can be only one, and I'd almost always want to use exclusive icon, simply because original image creator might not be aware of using it for ASF, or he might not be fine with it (even though it's very unlikely to happen).
Issue will be open for a few more days, and I think that eventually @stackia's icon will be used, as I don't have anything against that, neither I have any other contributions to choose from. If somebody is not happy with that outcome, he can always submit his own work for evaluation as long as this issue is open.
I, too, was thinking of putting "ASF" somewhere in the logo but I'm not really good at creating them (even if I like doing them).
@stackia's looks rather professional compared to whatever I could ever come up with, so I'm not even trying! =P
But I took the liberty to do a little modification to his, transforming those 3 vertical segments in "ASF".
It's just a quick work (made by hand) I did it mostly to give you the idea, I'm sure he can do it better if you want to accept this change (there should be plenty of "tall" fonts too, I just happen to have none installed on this machine).
The idea is to keep the "holes" in each letter as small/slim as possible so one can read ASF when using the bigger version and they kind of resemble the original vertical segments when using the smaller one:

EDIT: if you want more "entries" you should also expose this issue on the sg thread and/or in the steam group (I don't think I've read about this anywhere before).
The idea looks nice. Could you prepare one version with ASF text like @quappo pointed above @stackia? I'll then organize short voting whether people want clean version or with ASF text version and finally decide which one to use :smile:.
This tiny bit of text wouldn't be good visible for small icons. Just sayin'.
Most helpful comment
PSD & ICO:
ASF Icon.zip
Thanks for having such a great project enlighten our Steam community!