To be 'Reformed' should mean simply that your theology is constantly being reformed in line with Scripture.
Ecclesia reformata semper reformanda. A Reformed church is always in need of reformation. It shouldn't mean that your theology is permanently stuck in the 16th or 17th Century. However 'Reformed' folk will usually believe in Covenant theology and Cessationism.
Originally, the term meant that someone had left the Church of Rome and adopted Protestant theology. In France, for example, churches are described as being either 'Catholic' or 'Reformed.' However, those of us who describe ourselves as Reformed Baptist believe that whilst we follow in the footsteps of the Reformers and Puritans, we have abandoned the last relic of Romanist theology, infant baptism, I find the term 'Reformed' expresses my theology better than 'Particular' or 'Calvinistic.' although I find my theology very much in line with Keach, Coxe or Bunyan, though I reserve the right to disagree with them on various points.
Another reason that I use it is because it annoys some of the more sniffy Presbyterians (R. Scott Clark and others) who think they have patented the term.
Unfortunately the term 'Reformed Baptist' is being devalued these days and people who do not hold to covenant theology and who are charismatic are using it. It will probably end up being as meaningless as 'evangelical.'