Lioness Invitations: The Secret

Mrs. Hamster recently explained the importance of numbering your response cards.  Apparently it's quite common for guests to send in their RSVP and simply forget to put their name on it.  I'm sure we will have our fair share of RSVP errors, so if there's something we can do on our end to minimize the number of mishaps, I'm all for it!  I am definitely in favor of a little extra work to save my sanity in the long run.  Basically, I'm just trying to prevent this kind of a situation:

Source

The solution: invisible ink.  As Mrs. Cherry Blossom, Mrs. Socks, and Mrs. Sewing have previously discussed, this stuff is brilliant!  I found a set of two invisible ink pens on eBay for $2.00.  Each pen has a marker tip on one end and a little black light on the other.  We simply assigned each household a number on our guest list spreadsheet, then wrote the corresponding number on the back of each response card.  Invisible to the naked eye, yet very helpful to those with the right tools:

{personal photo}

Has anyone stumbled upon any other fun tricks to help make the RSVP process a little easier?