I read some discussion on this thread about whether or not to receive sacramental communion while visiting chuches. In churches that are theologically, doctrinally, and historically borne of the Protestant Reformation and that confess to yet follow the tenets derived from the Reformation (these are often called "Reformed" churches), quite a few of these "fence the table." If you are interested in receiving the bread and the wine, show up to church 15 minutes early and ask someone if you may speak to an elder who will give you "permission" to take the sacrament upon your confessed faith in Jesus Christ's saving grace. If you do not confess Jesus Christ, you are asked to abstain. The church takes the sacrament quite seriously and this procedure is set in place by them as a safeguard to protect you from harm (this stemming from Biblical text stating that worshippers in Corinth were dying from inappropriately -- without faith -- taking of the Lord's Supper). The "interview" with an elder ensures that you know what you're doing by receiving the sacrament.
In Reformed churches, the sacrament of the Lord's Supper is not merely a symbol but actually the spiritual nourishment of Christ's church. It serves to strengthen and advance the faith in Christ that the worshipper was first granted by grace.