Although both are considered forms of advertising - there is a night and day difference between textiles and signage. Both will carry their own inherent problems. To be involved with the garments and not be able to cut roll goods is foolish. Therefore buying the plotter was a smart thiing to do, especially for short runs and athletic goods.
Having done both we found that in the majority of situations:
1. Sign people do not feel that they make enough with textiles.
2. Textile people do not feel they make enough with signage.
Your key and focus should be on short runs. Now instead of having to sell to the customer that will only purchase 100 screened coroplast signs, you can offer the quantity of 10 or 25, etc. BUT you will see that people will try and get you to price just like the large screened quantities - something that is just NOT possible. You could also try and sell some banners. Small "quickie" signage. You will find that decals with anything other than a printer is a pain in the butt, and extremely labor intensive.
The biggest problem that you will face is your pricing structure. The structures from textiles and signage DO NOT mix. Textiles price on pennies and quantity, whereas signage is the opposite.
One of the biggest factors for this is the amount of money that gets invested for supplies and their shelf life. For example, you can buy a spool of thread and make a healthy margin EVEN if you do not use it all right away - it will not go bad sitting on the shelf. Even with screening, plastisol can go a long way for a little dollar amount.
With vinyl and substrates it is a different story. Vinyl should not be sitting around for more than six months. The adhesive can become degraded (like old gun powder). To get a good price on vinyl, you need to purchase 50 yard rolls. If you do not use that amount, it ends up in the trash - money down the drain. Stocked banners have a tendency to get trashed over time, etc. etc.
This is the biggest misconception regarding signage. People see the gross profit margin and assume that is net - far from it.
Okay - now we have told you some of the differences.
What plotter did you buy?
What software are you using?
(Put this in your profile as it will help later when you run across problems).
Have you ever applied vinyl before?
What quantity do you consider to be short runs?
Do you have your heat press yet? (If so, what size? If not look for a name brand 16x20 like a Hix)
Have you purchased any books in regards to signage?
Have you calculated any of your pricing yet?
These answers questions will help us better understand where you are.
BTW - Dan is correct. You should look into the screening. That will close the gap between your embroidered garments and your cut roll goods - there are very healthy margins in short run screening.
Hope this helps.