We do free software based on Python, Zope, Plone and related ecosystems.
We work in an enjoyable environment - we work where it is best. At the office, at home, in the park. We use conventions only for our programming techniques. We think that a programmer thrives if he gets his flexibility. As everybody depends on each other, we have a good and productive working climate.
There is no need at all to do something that applies the website design to the t-shirt.
Some additional thoughts on what we value: Teamwork, transparency, coding, transparency, prototyping, transparency, communicate good and often, and have a lot of fun doing this.
Finally also a statement evolved: "Syslab moves your content like wind on a turbine". Not necessarily to be on the shirt, but that is the idea behind the image.