Intended for the same purpose, i.e. discourage solicitors and deter unwanted visits, no-soliciting and no-trespassing signs differ in the degree of power they convey. No-soliciting signs are generally targeted more towards specific groups such as salespeople, fundraising individuals/groups, religious/political representatives, etc. On the other hand, no-trespassing signs target unwarranted visitors and warn them against wandering through your property.