Gomu Gomu no Stamp is a special technique that Monkey D. Luffy uses in the series of One Piece. It is written in Japanese as "ゴムゴムのスタンプ" (Gomu Gomu no Sutanpu), literally "Rubber Rubber Stamp". This attack will turn out to be a part of an extensive arsenal of rubber-based techniques Luffy possesses to support his powers from the Devil Fruit.
In Gomu Gomu no Stamp, Luffy simply stretches his leg and pounds his enemy with the sole of his foot. This technique is often used for a quick and powerful kick since the sudden extension of Luffy's limb may catch opponents off guard. Thus, the name "Stamp" was perfect for this attack, which literally looks like one was to forcefully stamp a rubber stamp on a surface.
With the many powers Luffy has attained throughout the series, so has the Gomu Gomu no Stamp. In Gear Second, he can do an advanced version called Gomu Gomu no Jet Stamp. This powered-up variation delivers the same effect as the Jet Pistol but with Luffy's foot instead of his fist. The Jet Stamp holds more speed and power than the original form, thus making the technique rather practical in Luffy's high-speed fighting style.
While the Gomu Gomu no Stamp is not among the more flashy of Luffy's attacks, it has, nonetheless, turned out to be very useful and effective in battle. The relative simplicity of this technique does, in fact, allow Luffy to use it in many different situations, which makes it a genuinely stalwart part of his repertoire. This further contrasts some of Luffy's more complex or visually striking techniques, outlining how his fighting style really does have balance between practical and spectacular moves.
The Gomu Gomu no Stamp has many fan interpretations and a lot of artistic renditions. On DeviantArt, an artist under the username LemynLime made his or her rendition of Luffy using the Gomu Gomu no Stamp, which only goes to prove the popularity of the technique with One Piece fans. Such types of engagement from fans aim to demonstrate that even Luffy's most simplistic techniques have turned out to make their mark on the audience viewing the series.
This technique has been featured in One Piece merchandise. The most famous example would be the "Luffy One Piece ATTACK MOTIONS BATTLE OF DEEP SEA" figure, depicting Luffy executing the Jet Stamp version of the attack. It is a collectible, allowing fans to further capture the dynamic motion of the technique that has very much cemented its place within the One Piece universe.
In the bigger picture of Luffy's fighting style, Gomu Gomu no Stamp symbolizes his ability to turn his rubber powers into applications for every fighting situation. It is not as destructive as techniques like the Gomu Gomu no Bazooka, nor is it really as symbolic as the Gomu Gomu no Pistol, but it does show just how creative Luffy can become with his stretchy body in offense and defense.
It is worth noting that the names and concepts of Luffy's techniques often inspire fan discourses and even social commentaries. One such discourse from a fan on social media, in jest, turned this technique into "Gomu gomu no acab stamp," playfully fusing Luffy's attack with the themes of social activism. Although this is not canon, it goes a long way to prove the effect One Piece, and its techniques, have had on popular culture.