It sounds like you're asking how you as an end user can post custom links from a supported HipChat client. The answer is that you can't.
As simoncpu pointed out, it is possible through the API to post a custom HTML message, which requires a separate application.
There are two ways:
On the HipChat clients, if you look at the 'users' list in the sidebar, the room admin will be displayed in bold letters.
On the website, if you go to https://hipchat.com/rooms, there is a 'room admin' column that lists this info.
Stuart McKeown helped me out. You have to:
Create public chat room.
Open Windows client
Open/Enter the public chat room you have created
Click on bottom right checkbox "Guest access is off". Clicking on it should change it to "on".
Note that you have to be Admin to be able to allow guest access.
Various size emoticons are used for display on various screen pixel densities, rather than actually showing the emoticon at different sizes. They cannot be accessed via a shortcut during chat, i.e. there is no (zoidberg@4x) or anything similar. I wish there was.
HipChat usually stores all content send on an Amazon Web Services's cloud instance used with the provider. To find the content you sent to someone, select the person in the people list and on the left there will be a panel listing all the files ever shared with that person. Click on the file name and it will either preview it for you or offer to download. ...