When I started freelancing 5 years ago, my accountant advised me to start with a large invoice number (eg: 20850) and increment for each new one :)

Decrementing from there would be more fun.

Fun indeed! Unfortunately illegal in France afaik.

When I started consulting, I initially made the date part of the invoice number, e.g., 04100501 was the first invoice sent on October 5th of 2004. This sidestepped the problem of showing customers how many invoices I had already sent. But it did show them how many I sent that day, which was usually not many.

I eventually switched to a sequential monotonic invoice numbering scheme for other reasons, mostly because it made it easier on the webapp I use for invoicing.

yymmdd<seq-#> is monotonically increasing. Though you could also just combine the first 6 or so digits of unix time and tack on a sequence number to the end of that.

i've heard of new companies doing that when ordering checks.

though strangely i've also seen other companies refuse checks below a certain number, as some sort of measure of credit worthiness.

I had always understood it to be the other way around. Companies won't accept checks below a certain number, so you just start your check run at an "acceptably high" number.

I have always done this with checks and with invoice numbers. I generally start at some number just over 10,000.

Perhaps your comment was meant to be light-hearted and I am just being pedantic, but all an interested party has to do is come back a few more times over the course of a few days and note the values of new IDs. At that point they know the rate at which you are (adding new customers/adding new content/whatever) and can project backwards from there (completely ignoring the absolute value of the initial ID.)

Would a repete customer really care what your rate is? If this is about impressions, the fact that they are returning indicates that you made a good enough impression that should far overshadow your invoicing rate.

I'm not not thinking about repeat customers. I am thinking about competitors and people looking to gather industry information.

The point, as stated by tptacek, is that sites quite often leak information.