||The only way to definitively identify LSD is to do laboratory testing of the material. However, there are two primary field tests available. The first is a chemical reagent test called "Ehrlich's Reagent" which is available online from a variety of sources. It can identify indoles, of which LSD is one. It does not definitively identify LSD, but can identify that LSD is not present.|
The second is a UV test based on the fact that LSD fluoresces (glows) blue to blue-ish white under longwave (360 nm) UV light. Obviously other things glow under blacklight as well, so just the fact that it glows doesn't mean it's LSD, but if it doesn't glow, LSD can generally be ruled out. The glow should be apparent in both crystal form and liquid form.
Whether or not this test can be successfully used to identify whether LSD liquid is present on other materials such as blotter or sugar cubes is more complicated. In a dark room, a blacklight held close to a freshly laid, reasonably strong (~100 ug) drop of LSD will glow prominently. However, if the concentration is low/weak enough, the glow doesn't appear. Additionally, many papers and inks can themselves glow under blacklight, so a fully glowing hit of blotter (rather than a glowing spot on the hit) doesn't necessarily identify the presence of LSD. That means that it can be more difficult to identify blotter that has been dosed by dipping the paper rather than dropping individual drops on each hit.
An additional issue, for materials sold as LSD after 2010 is that a new family of chemical, including 25I-NBOMe and 25C-NBOMe are also being sold on blotter. The blotter size and form is often indistinguishable from that used with LSD (1/4 inch x 1/4 inch perforated squares). Though there are some reports of the NBOMes fluorescing under UV light (glowing a pink or orangish color), Erowid found that a 0.1ml drop containing 1000 ug of 25I-NBOMe dissolved in 0.1 ml ethyl alcohol did not glow under either 365 nm or 254 nm blacklight. A vial of 25I-NBOMe in alcohol also did not glow. Be careful not to mistake blacklight reflection/refraction off of a glass vial for a glow. Also, many papers and inks can glow under UV by themselves, so blotter can glow in blacklight without any psychoactive chemicals being present.