UTCClock

Adds a clock displaying the current time in the UTC time-zone to the header on both Oasis and Monobook. This is helpful in figuring out how long ago comments were posted on talk pages and forums since the user's signature shows the time in UTC when it was posted.

Installation
Default appearance (English):

Custom appearance: This last syntax is the most powerful but that also makes it the most complicated. See the Instructions here.

It's also possible to position the clock inside the GlobalNavigation strip instead of the header if you want to do that:

Changing the Appearance
The clock element has the id, you can apply CSS rules to change the appearance:

Customising the Clock
The clock syntax is based on the C/C++ strftime function but slightly different. Basically,  takes an arbitrary block of text that will appear unchanged on the clock except for the magic   symbols. Each symbol has the following form: Type 1: %   Example: %d = Current day of the month, no minimum length (e.g. 2) %2d = Current day of the month, force it to always have at least 2 characters (e.g. 02) Type 2: % {}  Example: %{Sunday;Monday;Tuesday;Wednesday;Thursday;Friday;Saturday}w = Displays English day of the week Type 3: %% = Produces a single % symbol The last item in a list will be used for everything greater than the length of the list. If there are only 6 entries in a day of the week list then the last one (6th) will be used for both of the last 2 days of the week.

Unlike strftime there are no default minimum lengths. If you don't supply your own width number then it will always be only as wide as necessary, if you want the day of the month number to always be 2 characters wide then you must ask for that specifically using  instead of just.