I've assembled a serious collection of JTHM comics, and after receiving lots of wrongly identified "first prints" in the mail over the years, I am well suited to clarify this for everyone: First Printings of Johnny the Homicidal Maniac 1-7 are not marked explicitly as such. To check if you have a second printing: CHECK THE BOTTOM OF THE INSIDE BACK COVER. This is where early reprintings are marked, always using very large bold font underneath the ads for shirts/upcoming issues. Beginning with the 3rd/4th printings this info is moved into the front indicia where you'd expect to find it. SQUEE and the Bad Art Collection follows this same pattern: check the bottom of the inside back cover!
That is all you need to know to correctly identify them, but there are some telltale shortcuts that conform to these rules:
Issue #1 1st printing has a generic full page ad for a slave labor catalog on the inside back cover. 2nd printing on have ads for johnny merchandise.
Issue #2 first prints DO NOT HAVE A COVER PRICE OR ISSUE #. These were misprinted without the price and # on the front cover. This is an especially helpful shortcut when looking at ebay auctions of supposed first printings. If the picture of #2 has a coverprice/issue#, well... it's not a first printing.
Around printing 15 or so, Jhonen Vasquez redrew the SLG cover logo. If you see a picture of a supposed first printing that has the newer SLG logo then you are looking at a 21st print, not a 1st print.
I have also talked to SLG Publisher Dan Vado a couple of times at cons, asking him things like "What was the print run of the first printing of #1" and his answer was (paraphrasing) 'We always print 4 or 5000 copies of stuff like that" and he also told me that each time they reprint the books it's for about 5000 copies and each issue is getting reprinted like 3 times a year.
The "SPECIAL EDITION" of #1 is signed and numbered to 2000 copies. It came out around the time of the 4th printing of #1/1st printing of #4. I believe that some of the 2000 books were sent out unannounced to stores that ordered the current printing, but I haven't confirmed this with Vado. I believe this because I found one on the shelf at a store back in 1997 while checking their inventory for 1st prints. This particular store had about 50 copies of #1-4 in stock at the time and had probably sold about 100 copies before that, so they must have been one of SLG's best customers since most stores are cautious about heavily ordering new copies of B&W indie books. The cover is cardstock, and it is marked SPECIAL EDITION instead of having a cover price.
Even though there are only 2000 copies of the S.E. versus the supposed 5K 1st printing of #1, I've found that the Special Edition is a bit easier to find - Probably because they are easier to identify and most were set aside as something special as soon as it was printed, as opposed to the 1st print of #1 which from the cover looks like any other, and was not of collecting interest when first released, and became a cult hit precisely because people passed their copy around to friends, many of whom were not regular comic readers familiar with the gentle handling of comics. Furthermore the cardstock cover means the SE is typically in nicer condition. Since I see about 1.5 copies of the SE for every 1st printing of #1 offered for sale, I suspect Dan Vado might be misremembering the print run of the 1st printing of #1 and that it is actually closer to 3k than 5K. The first printings of #2-7 turn up fairly regularly and I'd guess print runs are probably in the 5000+ range.