It would have been removed because you've hotlinked your image from your Photobucket account

if you have a look at the upload page here it states:

Rules for posting images on Simviation's forums

* Please keep all screenshots/images in JPG (or GIF for small images) format & less than 150K.
* Please keep all images within 1024 pixels wide
* Please keep PERSONAL avatars (logo under your name) less than 10K & 100 pixels wide
* Please keep SIGNATURE images within 30K max.
* Please do not post more than 600K total of files in any one thread.

Important: Do not link to these images from other sites. Members found doing this may be banned & images deleted.

this would be why your sig and avatar keep disapearing... Also if you copy this link:
Code:

[img]http://www.simviation.com/yabbuploads/Denali2.jpg[/img] 

Into where you have already got your Photobucket link it will be your current avatar uploaded to the simviation servers... (also resized it for you to the forum specs and reduced the weight of the avatar too from 118kb to 1.42kb)

John