I used to work at a shelter & yes, sadly, people steal quite often. In some cases, one client would pull a weapon on another client in order to steal a nice blanket or quilt. You don't need to make it ugly, just simple. Sometimes women & children's shelters are better; it just depends.
Think Traditional Amish quilts. Nothing too light colored because it may travel around all over town & only get washed once a month, if that. Dark colors are good choices for that reason. A solid color whole cloth or basic large piecing would be nice. Nothing showy. Just stop for a moment & think to yourself "would I feel comfortable carrying this quilt while walking alone through the worst part of town? would it attract the wrong kind of attention?" If your answer is "no", you've come up with a good design. The main value in the quilts for the homeless is not their artistic quality, but the warmth the quilt gives, the reliability of having one's own bedding (shelters provide bedding at night, but if you get cold during the day or early evening, you're out of luck), and the health & sanitation benefits of not having to share bedding that was used the night before by a client with ringworm or bedbugs or such because not all volunteers are great at following washing protocol. Besides the fact that people suffering from mental illness or substance abuse are more likely to be homeless than the average healthy individual, others are simply greedy or desperate and a beautiful quilt that would sell for hundreds of dollars is more temptation than some can resist. A simpler quilt truly is a better gift in this case than a large elaborate one.
Bless you for your service to the homeless in your community. I'm sure your gift quilts will be greatly appreciated for many years to come.