Sadly you can't test a signature on these forums, once you upload it it appears on every one of your posts, not just new ones.
There is a difference in posting a big picture or even several in a topic where they only open if you open that topic and posting one in your signature where it is opened on every topic you have ever or will ever post to. Folks on limited data budgets can avoid the topics with big pictures after the first time, it is impossible to avoid every topic someone with a big picture in their profile has posted to.
For really huge pictures it is much kinder to post links to them with a note that they are big, that saves folks from getting a surprise.
I'd suggest that if you have a picture on a specific subject/topic just post it in the topic after reducing it (via crop and resize plus a moderate JPG compression level) to a reasonable size or post a link to it that the forum can reduce to a thumbnail. If you have a picture of your rig like some folks are using in their signature put it in your profile, put links to your on-line photo album there too if you want.