Hmmm. From what I've seen (and I've been around this business for 6 years now), the president is usually one of the check-signers. But, I know each group is different.
Does your group issue warrants (a.k.a. check authorizations, check request forms, etc.) for each check? It's a simple for that basically supports the check--it tells what the funds are being used for (event description, items, etc)--and more importantly, if the amount was approved in the budget or if it was voted on and approved during a meeting. If you don't sign checks, you should at least see and approve all of the check warrants/requests.
I think you should talk about this at your next meeting. It's not good business for the treasurer write checks without the approval of your board. If your treasurer and principal needed to pay for items without board approval, they could have paid for the luncheon with their own money, and then ask to be reimbursed at a board meeting.
I also agree with what Renee says--all checks should be written and signed at meetings. If you want a sample of the Check Authorization Form we use, write me at
annmoore@cox.net