Unique helipad numbers

[stugots945]

I'm doing a bit of research and ran into a wall. I understand that helipad numbers are the weight limit in thousands of pounds. However, rarely I notice other numbers or writings on a pad. For example, I saw one that had an 8 mark and then a very small box with a three digit number in it outside the main square.

 

Wondered if anybody knows what these mean and why they are on? Are there any other unique numbers that are used on pads? I did read that gov't buildings tend to have some sort of unique labeling but I haven't seen any and am not quite sure what would be the point of it.

 

Thanks.