You are welcome to use our logo. If you are planning on making money off of our logo (e.g. you want to make merchandise for sale with the logo ... t-shirts, coffee mugs, etc.), then you need to contact us for licensing information. For pretty much all other uses, there is no licensing requirement. For example: a logo on your website showing that you use/promote Joind.in, even commercial websites; course materials; a bunch of t-shirts for your own use and some friends, or your user group; a banner for your event; etc.. If in doubt, ask. However do not use the logo in such a way, that it suggests that a particular person, company, course, etc. is endorsed by Joind.in.