I'm with Patrick, more interested in the fact that a guy is steadying the wheel while another is swinging an axe at it!
Dave
This is an issue which has interested me for some time
As every photo I have down loaded from the AWM of a motorcycle in Australia either has the 5 digit number or no number on the Tank but every motorcycle in an overseas theatre has the contract number on the Tank but not the Asset number. its an issue I wanted to pursue in the research centre at the AWM when I was there recently but unfortunately I ran out of time preparing for my visit to the western front later this year so it will have to wait until I am next there unless someone knows the answer? I have seen some discussion on a site called Anzac Steel supporting this I have not been able to confirm the theory. 
email (option): Grumpy.moran@gmail.com
Dave
Each motorcycle taken on charge by the Australian Army would have had a Asset number but this looks like it was not transferred to the tank in overseas theatres and I can't be definite why those used in Country did not use the contract number on the tank of the Photographic evidence suggests that the Asset number (5 figure numerical code) was used on the tank in some cases although this is by no means universal indeed you see more home based machines with no identifying number like I said its an issue I would like to get to the bottom off but it would seem if your trying to represent a machine used in Australia then either the Asset number or no number is correct for machines used in the Middle East theatre then an appropriate contract number would be the go as for the south eastern Asia theatre I have no idea. But I will do some research when I have a moment.
the caveat to all this it is based solely on Photographic Evidence only and may very well be completely wrong 
email (option): Grumpy.moran@gmail.com
There are several interesting things in these photos 1 the top color photo shows the flag on the handlebars being the red ensign of Australia consistent with a similar flag passed on to me by my late father a souvenir of his service in Northern Territory at the time of the Japanese air raids the blue ensign currently used Did not become the official national flag until after the war ended .
In the bottom photo the group appear to be trying to straighten the frond end of the motorcycle using the only available tools being the pioneer tools available on a truck and the axe is the closest to a hammer suggesting it was being one somewhere on the Track rather than in a workshop environment great photos 
email (option): Grumpy.moran@gmail.com
Havent you seen the way the Assies use a tyre lever before?
TTJohn
email (option): Jomichael@aol.com
Exactly but it was also used to track service history &maintenance history in much the same way that the regimental number traced a soldiers history but it would appear that this could not be done with the C number alone as these are not unique to each vehicle?
email (option): Grumpy.moran@gmail.com