Default players are able to use command
I have enabled signartist.url for vip's only and default doesnt have the commands, but normal players are still able to use it. Is there anything you can think of what it could be? i've checked all the groups and still no joy.
Sounds like the default group has the permission for it. The signartist.url permission is only for the /sil command, every other command has its own permission. I'd suggest checking the default group with "oxide.show group default" to see if it has ANY of the signartist.* permissions.
it doesn't have it :S 

Group 'default' permissions:

nteleportation.home, nteleportation.deletehome, nteleportation.homehomes, nteleportation.tpr, trade.use, trade.accept, easyvote.use, randomrespawner.use, furnacesorter.allow, securitylights.use

Are you sure the "normal" player isn't in the VIP group with the permission, else another? You can check that player by using "oxide.show user USERNAMEORID" to see which permissions they have. They'd have to have the permission for the command to work, it will not work otherwise.
it's all default players are able to use it, ive logged onto a family shared account with no permissions bar default and it still has it. 

(01:51:16) | Player 'jackpiratee (76561198026143416)' permissions:

nteleportation.home, nteleportation.deletehome, nteleportation.homehomes, nteleportation.tpr, trade.use, trade.accept, easyvote.use, randomrespawner.use, furnacesorter.allow, securitylights.use

And how exactly are they using it?

Player 'DarkPrestige ' permissions:

nteleportation.home, nteleportation.deletehome, nteleportation.homehomes, nteleportation.tpr, trade.use, trade.accept, easyvote.use, randomrespawner.use, furnacesorter.allow, securitylights.use, kits.member

Player 'DarkPrestige ' groups:

default, member

Most players permissions look like this other than the vips which have it, but still they can use it.

typing /sil "url" and it just straight works.
Yeah, not really possible, so not sure what to say there. The permissions are required for the commands, so I don't see how it would work unless they somehow have the permission. There isn't anything this plugin can do differently, it is using the permission system properly and there are no other reports of it not working for many months.
This is what im saying im really not sure why this is happening. Ive got it clear that there are no permissions granted to these players from groups or by user privileges, and still its working for them. im stumped.

Merged post

Group 'default' permissions:

nteleportation.home, nteleportation.deletehome, nteleportation.homehomes, nteleportation.tpr, trade.use, trade.accept, easyvote.use, randomrespawner.use, furnacesorter.allow, securitylights.use

Group 'vip' permissions:

quicksort.use, deathmarker.use, signartist.url, signartist.text, signartist.restore, kits.vip

Group 'chatmod' permissions:

deathmarker.use, bgrade.1, quicksort.use, quicksort.lootall, signartist.url, signartist.text, signartist.restore, bgrade.3, bgrade.2, nteleportation.vip, betterchatmute.use

Group 'vip+' permissions:

bgrade.3, bgrade.2, bgrade.1, deathmarker.use, quicksort.use, signartist.url, signartist.text, signartist.restore

Group 'member' permissions:

kits.member

There are the groups and no user has any special permissions. So i have no idea.