First off, what you have to do is go down to your nearest secondhand shop and buy a pair of BROWN, not black, work slacks. Then ride home on a unicycle with the bag containing the slacks in your left hand while playing the trumpet with your nose with the right hand, playing to the tune of "She's A Bad Mamma Jamma" by the Ohio Players. Then when you return home you must sing an ancient negro spiritual while wearing a Brazilian fruit hat and a poncho and dancing the ancient Native American dance of the rainmaker. Then following the completion of the previous step you must take the secondhand slacks you purchased and light them on fire from the right pant leg up, leaving the pockets up unsinged. Then you must place the remains of the slacks on your head upside down like a crown over the fruit hat, walk over to your computer and demand that it change your BBS sig. If this does not work, you may have to threaten it with force by turning it on its side and opening the case whilst holding a large tool such as a hammer or screwdriver, as to scare it into submission. Then when it's at its peak of fear and indecisiveness, lunge at the opportunity by inserting your penis directly into the floppy drive and thrusting repeatedly, luring it into a deep coma. Now that you've got your computer under your will, take this free time to beat it repeatedly with a sack of oranges or rape it with whatever object is deemed fit. Then when you are finished, there is a small port inside the box of your power supply. This is the secret internal computer Grounds Gold menu. Be sure to not turn off the power after opening the power supply casing, as this will disable access to the Grounds Gold menu. Now to get in, you have to tap three times on the upper left casing four and one-half times. Then you have to whisper the password, which is "Turkmenistan". Following this, you will have entry to the internal GG menu, where you may change your sig to your free will. After completion of the sig changing you have to log out of the Grounds Gold menu by sticking your tongue directly into the power supply's left circuit. It may provide a small shock, but this is a sign that you have logged out. After that, you must shut the casing on your computer and masturbate heavily until you have ejaculated enough semnial fluid to keep the case closed for a long time. Then you have to turn the PC right-side up and give mouth to mouth with the floppy drive. This will awaken it from its deep coma. You will then have the ability to return to the NG BBS with a brand new signature picture, and a profound sense of accomplishment.
This has been a how-to on changing your signature picture on the Newgrounds BBS.