Mysterious Cards have started to pop up in the Steam marketplace, providing more hints that the Summer Sale is coming this month. I’m not trying to be enigmatic by calling them “Mysterious Cards,” that’s actually what they’re labelled as (see the image above.)
The cards were spotted on NeoGaf (and possibly other places too, but that’s where I saw it mentioned) and can apparently be crafted if you have certain trading card sets. That’s why there are several hundred of them for sale right now.
Thanks to a previously leaked image requesting that developers get their sale spreadsheets in by 13 June, we’ve been able to speculate before that the Steam Summer Sale will be starting in the mid-to-late period of that month (probably around the week beginning 23 June.) The recent appearance of Mysterious Cards adds a little weight to that, because we all know how much Valve love their sale-specific trading card games.
Update: Further indications of a 19 June start date have appeared today, courtesy of an online payment promotion. (Thanks to reader MorningLM for that one.)